As Sacks aged, he felt as if he were gazing at people from the outside. But he also noticed a new kind of affection for humans—“homo sap.” “They’re quite complex (little) creatures (I say to myself),” he wrote in his journal. “They suffer, authentically, a good deal. Gifted, too. Brave, resourceful, challenging.”

Perhaps because love no longer appeared to be a realistic risk—he had now entered a “geriatric situation”—Sacks could finally confess that he craved it. “I keep being stabbed by love,” he wrote in his journal. “A look. A glance. An expression. A posture.” He guessed that he had at least five, possibly ten, more years to live. “I want to, I want to ••• I dare not say. At least not in writing.”

In 2008, Sacks had lunch with Bill Hayes, a forty-seven-year-old writer from San Francisco who was visiting New York. Hayes had never considered Sacks’s sexuality, but, as soon as they began talking, he thought, “Oh, my God, he’s gay,” he told me. They lingered at the table for much of the afternoon, connecting over their insomnia, among other subjects. After the meal, Sacks wrote Hayes a letter (which he never sent) explaining that relationships had been “a ‘forbidden’ area for me—although I am entirely sympathetic to (indeed wistful and perhaps envious about) other people’s relationships.”

A year later, Hayes, whose partner of seventeen years had died of a heart attack, moved to New York. He and Sacks began spending time together. At Sacks’s recommendation, Hayes started keeping a journal, too. He often wrote down his exchanges with Sacks, some of which he later published in a memoir, “Insomniac City.”

“It’s really a question of mutuality, isn’t it?” Sacks asked him, two weeks after they had declared their feelings for each other.

“Love?” Hayes responded. “Are you talking about love?”

“Yes,” Sacks replied.

Sacks began taking Hayes to dinner parties, although he introduced him as “my friend Billy.” He did not allow physical affection in public. “Sometimes this issue of not being out became very difficult,” Hayes told me. “We’d have arguments, and I’d say things like ‘Do you and Shengold ever talk about why you can’t come out? Or is all you ever talk about your dreams?’ ” Sacks wrote down stray phrases from his dreams on a whiteboard in his kitchen so that he could report on them at his sessions, but he didn’t share what happened in therapy.

Kate Edgar, who worked for Sacks for three decades, had two brothers who were gay, and for years she had advocated for gay civil rights, organizing Pride marches for her son’s school. She intentionally found an office for Sacks in the West Village so that he would be surrounded by gay men living openly and could see how normal it had become. She tended to hire gay assistants for him, for the same reason. “So I was sort of plotting on that level for some years,” she told me.

In 2013, after being in a relationship with Hayes for four years—they lived in separate apartments in the same building—Sacks began writing a memoir, “On the Move,” in which he divulged his sexuality for the first time. He recounts his mother’s curses upon learning that he was gay, and his decades of celibacy—a fact he mentions casually, without explanation. Edgar wondered why, after so many years of analysis, coming out took him so long, but, she said, “Oliver did not regard his relationship with Shengold as a failure of therapy.” She said that she’d guessed Shengold had thought, “This is something Oliver has to do in his own way, on his own time.” Shengold’s daughter, Nina, said that, “for my dad to have a patient he loved and respected finally find comfort in identifying who he’d been all his life—that’s growth for both of them.”