They also had a three-way friendship with a classmate named David, who enlivened everyday hangouts with his spontaneity and zeal. Once, David realized there was no limit to what you could deep-fry, so he and Toly prepared batter, and the three of them deep-fried every edible item in Toly's kitchen. David also struggled with his mental health, and toward the end of high school and in college, Andrew and Toly, as they describe it, were his two "lifelines." David dropped out of college early into sophomore year and, while Toly was a junior, spent months sleeping on a mattress next to Toly's bed in his college apartment. He later stayed with Andrew. Hundreds of miles apart from each other at their respective colleges, Andrew and Toly regularly had calls, sometimes staying on the phone for hours, to talk about what was going on with their friend. David later died by suicide. Andrew and Toly made a pamphlet for his funeral, gave speeches to honor him, and gathered friends in the basement of Andrew's parents' house for a night of reminiscing and mourning. When they talk about David now, their voices don't drop into a somber register; instead, they marvel and chuckle when they call back memories of him. It helps that as they grieved, they had someone else who knew exactly what it was like to lose David.

After graduating from college in 2011, Andrew and Toly moved their lives in parallel. Looking to be helpful and, in part, inspired by David to think beyond conventional paths, they volunteered as software developers for the National Institute for Medical Research in Tanzania, living there together for seven months. Andrew says there was no one moment when he and Toly determined that their friendship went beyond what people typically mean by best friends. "Our commitment was almost more borne out by how we acted in moments where it could have fallen away," he says, especially during the two years they spent on opposite coasts. They spoke often and went on to become roommates in graduate school, where they studied soft matter physics in the same lab, and again when they cofounded a government transparency nonprofit. From living together to working together, they made deliberate decisions to organize their lives around each other. Andrew and Toly became a we.

Their closeness threw off some people who knew them. On a phone call when Andrew was about thirty years old, his mom, Lisa, asked him if he was gay. She said she wanted Andrew to know that if he and Toly were in a romantic relationship, she was fine with it. Though Andrew appreciated his mom's acceptance of a hypothetical same-sex romantic relationship, that's not what he and Toly had with each other. He thought he'd already made clear that he and Toly weren't romantically involved.

"Deep down inside," Lisa says, "I didn't think that it was a romantic relationship, because Andrew's not the type of person that would be shy about saying it was, if in fact it was." Andrew is also not the type of person to repress same-sex attraction, had he felt it. He and Toly regularly have marathon conversations in which they inspect their feelings and behavior with the fastidiousness of psychoanalysts. If he or Toly had sexual interest in the other, it would have come up.

Lisa says her confusion about the nature of Andrew and Toly's friendship "gnawed at me," but she retired her questions about it. She switched to asking Andrew if he was dating anyone. Andrew responded with a question of his own: Why was it so important to her that he was dating? She said she wanted him to have someone who could give him "emotional wholeness," someone he could go to if he had a problem or a hard decision to make. As a mother, she said, she would be happy to know there's somebody in her son's life who gives him that kind of fulfillment.

Andrew told her he already had all of that—with Toly.

"What do you mean?" Lisa asked.

Andrew described Toly as a "platonic life partner."

Lisa said, "I don't understand how your life partner can be someone who you aren't romantic with."

Andrew's friendship defied two widely held beliefs: that a partnership is, by definition, a romantic relationship, and that without a long-term romantic relationship, life is incomplete.

* * *

This is a book about friends who have become a we, despite having no scripts, no ceremonies, and precious few models to guide them toward long-term platonic commitment. These are friends who have moved together across states and continents. They've been their friend's primary caregiver through organ transplants and chemotherapy. They're co-parents, co-homeowners, and executors of each other's wills. They belong to a club that has no name or membership form, often unaware that there are others like them. They fall under the umbrella of what Eli Finkel, a psychology professor at Northwestern University, calls "other significant others." Having eschewed a more typical life setup, these friends confront hazards and make discoveries they wouldn't have otherwise.

They also had a three-way friendship with a classmate named David, who enlivened everyday hangouts with his spontaneity and zeal. Once, David realized there was no limit to what you could deep-fry, so he and Toly prepared batter, and the three of them deep-fried every edible item in Toly's kitchen. David also struggled with his mental health, and toward the end of high school and in college, Andrew and Toly, as they describe it, were his two "lifelines." David dropped out of college early into sophomore year and, while Toly was a junior, spent months sleeping on a mattress next to Toly's bed in his college apartment. He later stayed with Andrew. Hundreds of miles apart from each other at their respective colleges, Andrew and Toly regularly had calls, sometimes staying on the phone for hours, to talk about what was going on with their friend. David later died by suicide. Andrew and Toly made a pamphlet for his funeral, gave speeches to honor him, and gathered friends in the basement of Andrew's parents' house for a night of reminiscing and mourning. When they talk about David now, their voices don't drop into a somber register; instead, they marvel and chuckle when they call back memories of him. It helps that as they grieved, they had someone else who knew exactly what it was like to lose David.

After graduating from college in 2011, Andrew and Toly moved their lives in parallel. Looking to be helpful and, in part, inspired by David to think beyond conventional paths, they volunteered as software developers for the National Institute for Medical Research in Tanzania, living there together for seven months. Andrew says there was no one moment when he and Toly determined that their friendship went beyond what people typically mean by best friends. "Our commitment was almost more borne out by how we acted in moments where it could have fallen away," he says, especially during the two years they spent on opposite coasts. They spoke often and went on to become roommates in graduate school, where they studied soft matter physics in the same lab, and again when they cofounded a government transparency nonprofit. From living together to working together, they made deliberate decisions to organize their lives around each other. Andrew and Toly became a we.

Their closeness threw off some people who knew them. On a phone call when Andrew was about thirty years old, his mom, Lisa, asked him if he was gay. She said she wanted Andrew to know that if he and Toly were in a romantic relationship, she was fine with it. Though Andrew appreciated his mom's acceptance of a hypothetical same-sex romantic relationship, that's not what he and Toly had with each other. He thought he'd already made clear that he and Toly weren't romantically involved.

"Deep down inside," Lisa says, "I didn't think that it was a romantic relationship, because Andrew's not the type of person that would be shy about saying it was, if in fact it was." Andrew is also not the type of person to repress same-sex attraction, had he felt it. He and Toly regularly have marathon conversations in which they inspect their feelings and behavior with the fastidiousness of psychoanalysts. If he or Toly had sexual interest in the other, it would have come up.

Lisa says her confusion about the nature of Andrew and Toly's friendship "gnawed at me," but she retired her questions about it. She switched to asking Andrew if he was dating anyone. Andrew responded with a question of his own: Why was it so important to her that he was dating? She said she wanted him to have someone who could give him "emotional wholeness," someone he could go to if he had a problem or a hard decision to make. As a mother, she said, she would be happy to know there's somebody in her son's life who gives him that kind of fulfillment.

Andrew told her he already had all of that—with Toly.

"What do you mean?" Lisa asked.

Andrew described Toly as a "platonic life partner."

Lisa said, "I don't understand how your life partner can be someone who you aren't romantic with."

Andrew's friendship defied two widely held beliefs: that a partnership is, by definition, a romantic relationship, and that without a long-term romantic relationship, life is incomplete.

* * *

This is a book about friends who have become a we, despite having no scripts, no ceremonies, and precious few models to guide them toward long-term platonic commitment. These are friends who have moved together across states and continents. They've been their friend's primary caregiver through organ transplants and chemotherapy. They're co-parents, co-homeowners, and executors of each other's wills. They belong to a club that has no name or membership form, often unaware that there are others like them. They fall under the umbrella of what Eli Finkel, a psychology professor at Northwestern University, calls "other significant others." Having eschewed a more typical life setup, these friends confront hazards and make discoveries they wouldn't have otherwise.