Kami West had been dating her current boyfriend for a few weeks when she told him that he was outranked by her best friend. West knew her boyfriend had caught snatches of her daily calls with Kate Tillotson, which she often placed on speaker mode.

But she figured that he, like the men she’d dated before, didn’t quite grasp the nature of their friendship. West explained to him, “I need you to know that she’s not going anywhere. She is my No. 1.” Tillotson was there before him, and, West told him, “she will be there after you. And if you think at any point that this isn’t going to be my No. 1, you’re wrong.”

If West’s comments sound blunt, it’s because she was determined not to repeat a distressing experience from her mid-20s. Her boyfriend at that time had sensed that he wasn’t her top priority. In what West saw as an attempt to keep her away from her friend, he disparaged Tillotson, calling her a slut and a bad influence.

After the relationship ended, West, 31, vowed to never let another man strain her friendship. She decided that any future romantic partners would have to adapt to her friendship with Tillotson, rather than the other way around.

West and Tillotson know what convention dictates. “Our boyfriends, our significant others, and our husbands are supposed to be No. 1,” West told me. “Our worlds are backward.”

In the past few decades, Americans have broadened their image of what constitutes a legitimate romantic relationship: Courthouses now issue marriage licenses to same-sex couples, Americans are getting married later in life than ever before, and more and more young adults are opting to share a home rather than a marriage license with a partner.

Despite these transformations, what hasn’t shifted much is the expectation that a monogamous romantic relationship is the planet around which all other relationships should orbit.

By placing a friendship at the center of their lives, people such as West and Tillotson unsettle this norm. Friends of their kind sweep into territory typically reserved for romantic partners: They live in houses they purchased together, raise each other’s children, use joint credit cards, and hold medical and legal powers of attorney for each other. These friendships have many of the trappings of romantic relationships, minus the sex.

Despite these friendships’ intense devotion, there’s no clear category for them. The seemingly obvious one, “best friend,” strikes many of these committed pairs as a diminishment.

Adrift in this conceptual gulf, people reach for analogies. Some liken themselves to siblings, others to romantic partners, “in the soul-inspiring way that someone being thoughtful about loving you and showing up for you is romantic,” as the Rutgers University professor Brittney Cooper describes some of her friendships in her book Eloquent Rage.

Some alternate between the two comparisons. From the night Joe Rivera and John Carroll met at a gay bar in Austin, Texas-Rivera was the emcee for a strip competition, and Carroll won the $250 cash prize-they felt like brothers. “Brothers that really want to hang out and be around each other,” Carroll clarified. Yet when Carroll considered their shared domestic life, he told me that “we have a little married-couple thing going on even though we’re not married.” These mixed analogies suggest that neither wedlock nor siblinghood adequately captures what these friendships feel like.

Many of those who place a friendship at the center of their life find that their most significant relationship is incomprehensible to others.

Intimate friendships don’t come with shared social scripts that lay out what they should look like or how they should progress. These partnerships are custom-designed by their members. Mia Pulido, a 20-year-old student at Drew University, says that she and her “soul mate,” Sylvia Sochacki, 20, have cobbled together role models in what has felt like a “Frankenstein” process: Through reading about intimate female friendships from centuries ago, the pair discovered a framework for a relationship that doesn’t neatly fit the contemporary labels of romantic or platonic.

They found their complementary personalities reflected in the characters Sherlock and Watson, and they embraced the casual affection (and the terms of endearment “Bubble” and “Spoo”) that they came across in a note between a wife and husband; it was tucked into a used book they found at a garage sale. Pulido has found it freeing to build a relationship around the needs and desires of Sochacki and herself, rather than “having to work through this mire of what society has told you this relationship consists of.”

Many of those who place a friendship at the center of their life find that their most significant relationship is incomprehensible to others. But these friendships can be models for how we as a society might expand our conceptions of intimacy and care.

When Tillotson and West met as 18-year-olds, they didn’t set out to transgress relationship norms. They were on a mission to conform, aye ma’am-ing their way through Marine Corps boot camp in South Carolina, and referring to each other by their last name preceded by the title “Recruit.” Most evenings, Recruit Tillotson and Recruit West spent their hour of free time chatting in front of their shared bunk bed.

During these conversations, they discovered that West’s mom had just moved to a city that was a 20-minute ride away from Tillotson’s hometown of Tulsa, Oklahoma. West and Tillotson spent boot camp’s month-long break together, winding through the Tulsa suburbs in West’s mother’s black sedan, late-aughts rap pulsing through the rolled-down windows.

For most of the next four years, they were stationed thousands of miles apart, including when Tillotson eventually deployed to Iraq. From afar, they coached each other through injuries, work woes, and relationship problems. Their friendship really blossomed once they both ended up in the Tulsa area for college, and they started to spend nearly every day together. By then, Tillotson was waiting for her divorce paperwork to be notarized, and West was a single mother caring for her 3-year-old, Kody.

When West got a job at a bar, Tillotson watched Kody during the day so her friend could sleep. Tillotson frequently joined West at preschool pickup. When the two women would walk down the hallway, past the miniature lockers, West said, “it was like the seas parted.” Tillotson could feel the parents’ eyes on her. Periodically, a teacher would sidle up to the two women, direct her gaze toward Tillotson, and ask, “Who is this?”

“People would always ask us how we know each other, or, ‘Are you sisters?’ A lot of times people think we’re dating,” Tillotson, 31, said. It would take too long for West and Tillotson to explain the complexity and depth of their friendship to every curious questioner.

With no lexicon to default to, people with friendships like West and Tillotson’s have assembled a collage of relationship language. They use terms such as best soul friend, platonic life partner, my person, ride or die, queerplatonic partner, Big Friendship.

For some, these names serve a similar purpose as matching friendship necklaces-they’re tokens mainly meant for the two people within the friendship. Others, such as West and Tillotson, search for language that can make their relationship lucid to outsiders.

West and Tillotson realized that people understand boot camp to be an intense setting, the kind of environment that could breed an equally intense friendship. When the friends began to refer to each other as “boot-camp besties,” people’s confusion finally faded.

For more than a decade, Nicole Sonderman didn’t mind if the only people who understood her friendship with Rachel Hebner were the two women who were part of it. Sonderman sums up their relationship as “having a life partner, and you just don’t want to kiss them.”

In the years when they both lived in Fairbanks, Alaska, the friends were fluent in the language of each other’s moods and physical changes. Before Hebner suspected that she might be pregnant, Sonderman made her buy a pregnancy test, steered her into the bathroom, and sat in the adjacent stall as Hebner took it. Four years later, the roles reversed: Hebner had the same accurate premonition about Sonderman. “We paid more attention to each other than we did to ourselves,” Sonderman, 37, told me.

They occasionally navigated around other people’s confusion about or combativeness toward their friendship. Their preferred term of endearment for each other, wife, wasn’t a problem for Sonderman’s then-husband. But once Hebner divorced her husband and started dating, her romantic partners got jealous, especially the women she dated. Sonderman grudgingly placated them by calling Hebner “wiffles” instead of wife.After those years in Alaska, the pair spent a few years several time zones apart, as Sonderman and her then-husband moved around for his work.

Eventually Sonderman moved back to Alaska, but Hebner had relocated to Indiana. Phone calls and occasional visits became their friendship’s support beams. Sonderman said that Hebner reached out less and less as she grappled with a cascade of difficulties: She was in an abusive romantic relationship and she lost her job because she had no one else to take care of her daughter while she worked. She was depressed. In October 2018, Hebner died by suicide.

For Sonderman, Hebner’s death was devastating. The women had envisioned one day living near each other in Alaska, where the two of them had met, and where Hebner longed to return. Now Sonderman had none of that to look forward to. For six months after Hebner’s death, she kept earphones in when she went to the grocery store. She couldn’t bear small talk.

Sonderman found it hard to translate her grief to others. “Most people don’t understand. They’ll just be like, ‘Oh yeah, I had a friend from high school who died’ or something and try to relate. But it doesn’t really resonate with me.” In other cases, people would impose a salacious and inaccurate story line onto their relationship to try to make sense of it. Because Hebner was bisexual, Sonderman said, some people believed that they were secretly lovers, and that Sonderman was closeted.

To Elizabeth Brake, a philosophy professor at Rice University whose research focuses on marriage, love, and sex, Sonderman’s experience is not just tragic but unjust. Because friendship is outside the realm of legal protection, the law perpetuates the norm that friendships are less valuable than romantic relationships.

This norm, in turn, undermines any argument that committed friendships deserve legal recognition. But if, for example, the law extended bereavement or family leave to friends, Brake believes we’d have different social expectations around mourning. People might have understood that, for Sonderman, losing Hebner was tantamount to losing a spouse.

With no legal benefits or social norms working in her favor, Sonderman has felt most understood by other people who’ve had an intimate friendship. Sonderman described one such friend who was an especially attentive listener. For two hours, he and Sonderman sat in a car, engine off, in a grocery-store parking lot. She talked with him about Hebner, cried about Hebner. Her friend said, “It sounds like she broke your heart.” Sonderman told me, “That was the first time that anybody really got it.”

Intimate friendships have not always generated confusion and judgment. The period spanning the 18th to early 20th centuries was the heyday of passionate, devoted same-sex friendships, called “romantic friendships.” Without self-consciousness, American and European women addressed effusive letters to “my love” or “my queen.” Women circulated friendship albums and filled their pages with affectionate verse.

In Amy Matilda Cassey’s friendship album, the abolitionist Margaretta Forten inscribed an excerpt of a poem that concludes with the lines “Fair friendship binds the whole celestial frame / For love in Heaven and Friendship are the same.”

Authors devised literary plot lines around the adventures and trials of romantic friends. In the 1897 novel Diana Victrix, the character Enid rejects a man’s proposal because her female friend already occupies the space in her life that her suitor covets. In words prefiguring Kami West’s, Enid tells the man that if they married, “you would have to come first. And you could not, for she is first.”

Two well-known women who put each other, rather than a husband, first were the social reformer Jane Addams and the philanthropist Mary Rozet Smith. In Addams’s bedroom, now an exhibit at the Jane Addams Hull-House Museum, in Chicago, an enormous portrait of Smith hangs above the mantle.

After meeting in 1890 at the pioneering settlement house that Addams co-founded, the women spent the next 40 years entwined, trudging through moments they spent apart.

During one separation, Addams wrote to Smith, “You must know, dear, how I long for you all the time, and especially during the last three weeks. There is reason in the habit of married folks keeping together.” When Addams traveled without Smith, she would sometimes haul the painting with her. When the two women journeyed together, Addams wired ahead to request a double bed.

No scandal erupted in the newspaper. These women weren’t pressed, directly or implicitly, about their sex lives, nor did they feel compelled to invent a label to make sense of their relationship to onlookers, as West and Tillotson would about a century later. Same-sex intimacy like theirs was condoned.

These friendships weren’t the exclusive province of women. Daniel Webster, who would go on to become secretary of state in the mid-1800s, described his closest friend as “the friend of my heart, the partner of my joys, griefs, and affections, the only participator of my most secret thoughts.” When the two men left Dartmouth College to practice law in different towns, Webster had trouble adjusting to the distance.

He wrote that he felt like “the dove that has lost its mate.” Frederick Douglass, the eminent abolitionist and intellectual, details his deep love for his friends in his autobiography. Douglass writes that when he contemplated his escape from slavery, “the thought of leaving my friends was decidedly the most painful thought with which I had to contend. The love of them was my tender point, and shook my decision more than all things else.”

One question these friendships raise for people today is: Did they have sex? Writings from this time, even those about romantic relationships, typically lack descriptions of sexual encounters. Perhaps some people used romantic friendship as a cover for an erotic bond.

Some scholars in fact suspect that certain pairs had sex, but in most cases, historians-whose research on the topic is largely confined to white, middle-class friends-can’t make definitive claims about what transpired in these friends’ bedrooms. Though we will never know the exact nature of every relationship, it’s clear that this period’s considerably different norms around intimacy allowed for possibilities in friendship that are unusual today.

A blend of social and economic conditions made these committed same-sex friendships acceptable. Men and women of the 19th century operated in distinct social spheres, so it’s hardly shocking that people would form deep attachments to friends of their own gender. In fact, women contemplating marriage often fretted about forging a life with a member of what many deemed the “grosser sex.”

“You would have to come first. And you could not, for she is first.”

Beliefs about sexual behavior also played a role. The historian Richard Godbeer notes that Americans at the time did not assume-as they do now-that “people who are in love with one another must want to have sex.” Many scholars argue that the now-familiar categories of heterosexuality and homosexuality, which consider sexual attraction to be part of a person’s identity, didn’t exist before the turn of the 20th century. While sexual acts between people of the same gender were condemned, passion and affection between people of the same gender were not.

The author E. Anthony Rotundo argues that, in some ways, attitudes about love and sex, left men “freer to express their feelings than they would have been in the 20th century.” Men’s liberty to be physically demonstrative surfaces in photos of friends and in their writings. Describing one apparently ordinary night with his dear friend, the young engineer James Blake wrote, “We retired early and in each others arms,” and fell “peacefully to sleep.”

Physical intimacy among women also didn’t tend to be read as erotic. Even men wrote approvingly of women’s affectionate relationships, in part because they believed that these friendships served as training grounds for wifehood. In his 1849 novel, Kavanagh, Henry Wadsworth Longfellow casts a friendship between two female characters as “a rehearsal in girlhood of the great drama of a woman’s life”-the great drama, naturally, being marriage to a man.

Men could feel unthreatened by these friendships because few women were in the financial position to eschew the economic support of a husband in favor of a female companion. By the late 1800s, exceptions to this rule started to sprout. Colleges and professions were opening up to middle-class (and, almost exclusively, white) women, enabling these graduates to support themselves, no husband required.

At this point, the historian Lillian Faderman told me, women’s intimate friendships “no longer had to be a rehearsal in girlhood.” Educated women could instead live together in what were called Boston marriages. These committed relationships allowed women to pursue careers and evade heterosexual marriage.

From the late 1800s to the 1920s, each one of these components-gender-segregated society, women’s economic dependency, the distinction between sexual behavior and identity-was pulled like a Jenga brick from the tower of romantic friendship. Men and women’s divergent social spheres began to look more like a Venn diagram, enabling emotional intimacy between the genders.

With far more women in the workforce and potentially independent, men weren’t so enchanted by women’s intimate relationships. Sexologists declared same-sex desire-not merely same-sex sexual acts-perverse. Americans came to fear that kissing or sharing a bed with a friend of the same gender was a mark of “sexual inversion.” Romantic friendships had lost their innocence.

A few decades after the erosion of romantic friendship began, Americans’ conception of marriage shifted. The Northwestern University psychologist Eli Finkel identifies three distinct eras in American marriages. The first, running from the colonial period until about 1850, had a pragmatic focus on fulfilling spouses’ economic and survival needs; the second, lasting until about 1965, emphasized love.

Finkel makes the case that starting around 1965, the “self-expressive marriage” became the ideal; spouses expected their partnership to be the site of self-discovery and personal growth. (Excluded from these structures for most of the nation’s existence were the tremendous number of Americans who were denied access to legal marriage, namely enslaved Black Americans, interracial couples, and same-sex couples.)

Throughout this evolution, Americans started relying more and more on their spouses for social and emotional support, with friendships consigned to a secondary role.

John Carroll, who met his platonic partner, Joe Rivera, at a gay bar, describes this type of romantic relationship as “one-stop shopping.” People expect to pile emotional support, sexual satisfaction, shared hobbies, intellectual stimulation, and harmonious co-parenting all into the same cart.

Carroll, 52, thinks this is an impossible ask; experts share his concern. “When we channel all our intimate needs into one person,” the psychotherapist Esther Perel writes, “we actually stand to make the relationship more vulnerable.” Such totalizing expectations for romantic relationships leave us with no shock absorber if a partner falls short in even one area.

These expectations also stifle our imagination for how other people might fill essential roles such as cohabitant, caregiver, or confidant.

Carroll and Rivera, 59, escaped this confined thinking. They built their lives around their friendship-at times deliberately, at times improvising in the face of unanticipated events. In 2007, Carroll discovered that the house next door to his was up for sale.

He called Rivera with an entreaty: “Bitch, buy that house, and you can just walk home from dinner!” Rivera would no longer have to drive across Austin several times a week to have dinner at Carroll’s house. Carroll, who’s a real-estate agent, had already filled out the contract for the house for his friend. Rivera just needed to sign.

After buying the house, Rivera did in fact log fewer miles in traffic, but that was a trivial benefit compared with the life-altering ones that came later. When Rivera became concerned that Carroll’s drug and alcohol use had gotten out of hand, he took photos of partiers entering and leaving Carroll’s house at 3 or 4 a.m.

Rivera staged an intervention with Carroll’s other friends, and Carroll agreed to get help before Rivera could even begin reading aloud the two-page letter he’d written. The next day, Rivera drove Carroll to a recovery center, and cried as he filled out the paperwork. Rivera asked the man who ran the center, “What if [Carroll] goes through recovery and when he comes out, he hates me for doing this to him?”

Their friendship did change after Carroll finished the program, but not as Rivera had feared. While Carroll was in recovery, he and his friends came up with a plan to turn his house into a sober home for gay men-a solution to Carroll’s shaky finances that also served a meaningful purpose. Once Carroll finished his own stint in a sober home, Rivera suggested that Carroll move in with him.

By the time Carroll unloaded his bags, Rivera was already months into his own sobriety, a commitment he made even though he never had an alcohol problem. Rivera said, “I didn’t want to be drinking a glass of wine in front of John when he couldn’t have one.” “Who does that?” Carroll asked, his voice blending incredulity and gratitude. They’ve both been sober for a decade.

Companionate romantic relationships and committed friendships appear to be varieties of the same crop, rather than altogether different species.

A friendship like theirs, which has spanned nearly their entire adulthood and functioned as the nucleus of their support system, raises a fundamental question about how we recognize relationships: On what basis do we decide that a partnership is “real”? It’s a question the journalist Rebecca Traister poses in her book All the Single Ladies, when she examines the central role that friends often play in single women’s lives. “Do two people have to have regular sexual contact and be driven by physical desire in order to rate as a couple?

Must they bring each other regular mutual sexual satisfaction? Are they faithful to each other?” she writes. “By those measures, many heterosexual marriages wouldn’t qualify.” At the same time, people who have intimate friendships are eager to declare their devotion. The social theorist bell hooks writes that women who have such close friendships “want these bonds to be honored cherished commitments, to bind us as deeply as marriage vows.” Companionate romantic relationships and committed friendships appear to be varieties of the same crop, rather than altogether different species.

Brake, the philosopher, takes issue not just with cultural norms that elevate romantic relationships above platonic ones, but also with the special status that governments confer on romantic relationships. Whereas access to marriage currently hinges on (assumed) sexual activity, Brake argues that caregiving, which she says is “absolutely crucial to our survival,” is a more sensible basis for legal recognition.

She proposes that states limit the rights of marriage to only the benefits that support caregiving, such as special immigration eligibility and hospital visitation rights. Because sexual attraction is irrelevant to Brake’s marriage model, friends would be eligible.

In LGBTQ circles, placing a high value on friendship has long been common. Carroll, Rivera, and several other people I interviewed for this story, absorbed the idea of “chosen family”—that those besides blood can decide to become kin—from this community. Though he and Rivera never considered dating, Carroll had already learned to be at ease with nonsexual intimate relationships with men. In other words, he had come to appreciate something that was once widely understood—as Godbeer, the historian, puts it, that “we can love without lusting.”

In many ways, Americans are already redefining what loving and living can look like. Just in the past several months, experts and public intellectuals from disparate ideological persuasions have encouraged heterosexual couples to look to the queer and immigrant communities for healthy models of marriage and family.

The coronavirus pandemic, by underscoring human vulnerability and interdependence, has inspired people to imagine networks of care beyond the nuclear family. Polyamory and asexuality, both of which push back against the notion that a monogamous sexual relationship is the key to a fulfilling adult life, are rapidly gaining visibility. Expanding the possible roles that friends can play in one another’s lives could be the next frontier.

Other changes in American households may be opening up space for alternative forms of committed relationships. Fewer and fewer Americans can count on having a spouse as a lifelong co-star. By the time they’ve gotten married-if they’ve done so at all-most Americans have spent a considerable part of their adulthood single. The tally of Americans’ unpartnered years grows once you tabulate the marriages that end because of divorce or a spouse’s death (about one-third of older women are widowed). According to a 2017 Pew Research Center report, 42 percent of American adults don’t live with a spouse or partner.

We’re also in the midst of what former Surgeon General Vivek Murthy has called a growing public-health crisis in the United States: loneliness. In a 2018 survey, one-fifth of Americans reported always or often feeling lonely.

Being alone does not portend loneliness-nor does being partnered necessarily prevent loneliness-but these data suggest that plenty of people would appreciate a confidant and a regular dose of physical affection, needs only amplified by the pandemic. Americans, who’ve long been encouraged to put all their eggs in the marriage basket, may come to rely upon a wider array of social relationships out of necessity.

A platonic partnership may not feel right for everyone, and as is true with dating, even those who want a mate might not be able to find a suitable one. But these relationships have spillover benefits for those in close proximity to them.

Tillotson told me that she thinks all her relationships have been brightened by her closeness with West. Their romantic partners appreciate that the friendship lessens their emotional load; their mutual friends treat Tillotson and West as a reliable unit to turn to when they’re in need; their veteran community has been strengthened by the volunteering they’ve done together.

Their platonic partnership fits Godbeer’s description of how Americans viewed friendship centuries ago, that it “not only conferred personal happiness but also nurtured qualities that would radiate outward and transform society as a whole.” Though Tillotson and West’s relationship serves these broader purposes, they choose to be bound to each other primarily for the joy and support they personally receive.

Tillotson thinks of her romantic partner as “the cherry on the cake.” She and West, she explained, “we’re the cake.”