I often see this book referred to as an "autobiographical novel," which seems like an odd term to me. The character's voice and circumstances feel awfully similar to Myles's own voice and circumstances (from what I know of them, at least)--she's a working class Irish girl growing up in Boston, a tomboy, grappling with her sexual identity, and becomes a poet--not to mention that her name is Eileen Myles. So maybe the facts aren't 100% accurate. It's still kind of a strange category. Aren't most novels a bit autobiographical, in that the author can't help but include part of themselves in it in some way? And I'll bet that most memoirs aren't wholly accurate either, simply because memory is funny in that way.
Regardless of category, whether fact or fiction, this book is moving, insightful, funny, lyrical--all those adjectives you use in book reviews. Told in a series of snapshots, moving back and forth through time, it definitely feels like a novel written by a poet (which it is, obviously), but this is a good thing.