Joe LeSueur and Frank O'Hara became friends in 1951, after meeting at a party given by John Ashbery where, as LeSueur recalls, "Tchaikovsky's Third Piano Concerto was played at full volume on John's portable phonograph." In 1955, LeSueur moved in with O'Hara—ostensibly while he looked for an apartment—and ended up living with the poet for nearly a decade. "I just came for the weekend and stayed longer than I usually did," he writes with the offhand candor that is his operative style.

The two went on to share four apartments, skipping from East Forty-ninth Street to University Place to East Ninth Street (before the days of the East Village's gentrification) and ending up at 791 Broadway, overlooking Grace Church. This haphazard, winning memoir is, as its title suggests, less a cohesive account of a life than a snapshot-series of a way of living. What's notable, of course, is how modern that way of living still looks, if you strike the Tchaikovsky; O'Hara and the New York School essentially invented our cultural idea of literary New York City as a place of campy wit and strong feeling, of banter and inventive art executed at high speed. No one may have embodied this paradox of intensity and play, of irony and belief, more fully than O'Hara: James Schuyler called him "an electric storm"; Joe Brainard famously spoke of his "light and sassy" walk; Harold Brodkey wrote about the "velocity of his will"; O'Hara's conversational poems speak for themselves.

To write well about life with a person more famous than oneself requires a peculiar mix of narcissism and humility—not a problem for LeSueur, a handsome blond Californian sometime-writer, consummate cruiser, and full-time flaneur. (LeSueur died in 2001, before his book was published.) Though he and O'Hara were only occasional lovers, each was the other's closest friend and companion. But fidelity was never the point: The sole thing in their apartment as prodigious as O'Hara's poetic talent was LeSueur's appetite for new, well-built men. (O'Hara was not shy in this regard either.)

Though Digressions lacks varnish—it's more scattily anecdotal than coherent—it's full of intimate glimpses of the sort that no biographer can reproduce. LeSueur recalls O'Hara rubbing lanolin on his skin several times a day regularly, to keep it fresh and youthful, and encouraging LeSueur to do the same; he remembers struggling to write while O'Hara sat down at noon at his Royal typewriter and pecked out a "longish" one-act play by cocktail hour—"which came rather early on Saturdays." LeSueur, who was something of a hanger-on in the painting world that O'Hara moved effortlessly through, nonetheless offers quick sketches of seminal figures—Jane Freilicher, Lee Krasner, Willem de Kooning—that are usually delightfully gossipy, if never exactly objective. About Yukio Mishima, for example, whom LeSueur met a handful of times before the Japanese novelist committed hara-kiri, he writes, "I decided that the gifted Yukio Mishima must be a size queen; and now, thirty-odd years later, cognizant of the direction his life took after 1957, I can't resist considering the possibility, admittedly far-out, that his apparent preoccupation with big cocks was so great that it might provide us with one key to understanding why he did what he did."

LeSueur paints a familiar portrait of O'Hara as a man almost impossibly enthusiastic, curious, and sensitive to others (though he was capable of great cruelty as well, especially in his most bourbon-soaked days). One anecdote is particularly touching: When the husband of the mom-and-pop corner grocery died, LeSueur made an awkward apology, fled the shop, and gave the news to O'Hara; soon afterward, the poet went out to get some cigarettes and didn't come back for over an hour; upon his return he said only that he'd gone for a long walk. When LeSueur later asked the deli woman (who thought that the two were brothers) about it, she revealed that Frank had come to express his condolences and that the two had sat and talked at length. "Your brother made it all right, Sonny," she tells LeSueur. But LeSueur also delivers a substantive picture of the poet as an influential curator at MOMA—a critic who helped make Joseph Cornell's name and who saw beyond other critics' dismissal of early Rauschenberg, who above all loved to write about painting. LeSueur witnessed O'Hara's work from a distance, but he writes simply and accurately about O'Hara's taste and wit.

LeSueur doesn't synthesize primary source material the way David Lehman did in The Last Avant-Garde, and his critical readings of O'Hara's poems are weak (for better close readings of the poems, see Marjorie Perloff's Frank O'Hara, Poet Among Painters); for a biography of O'Hara, readers may want to turn to Brad Gooch's City Poet (a book that many of O'Hara's friends dislike, because of its emphasis on the poet's descent into alcoholism). But this is the kind of partial, personal, strange document no other writer could replicate; a love letter to the memory of the privilege of his unique arrangement with O'Hara. Though the two ultimately grew apart together—LeSueur moved out in 1965, shortly before Frank's death—LeSueur, fully capable of being petty, is never less than elegant in his appreciation of O'Hara: "Nothing momentous happened. Yet a day in which I spent an hour or so with him would become transformed and hold some special promise. What he did to bring this about, what alchemy he practiced so effortlessly, I still find difficult to fathom and impossible to describe."

Meghan O'Rourke is senior editor of Slate.