Ten years ago, the gay-friendly high school of David Levithan’s playful first novel, “Boy Meets Boy,” seemed a hopeful “some day.” Now his 16th book, “Two Boys Kissing,” reflects a contemporary America that, while still fraught, is clearly the more open “future few of us would have imagined.” To protest a recent hate crime, Harry and Craig decide to stage a public affirmation of love by breaking the Guinness World Record for the longest kiss. But a lot can happen during the necessary “thirty-two hours, twelve minutes, and ten seconds,” including complicated feelings, exhaustion, cramps, angry parents and egg-throwing hecklers. Their story is intercut with those of other gay teens: the blossoming romance between Ryan and transgendered Avery; the ups and downs of Peter and Neil’s long-term relationship; and the increasing desperation of Cooper, a recently outed runaway. Over the years, Levithan has consistently explored new creative territory, including collaborations with popular young-adult novelists John Green (“Will Grayson, Will Grayson”) and Rachel Cohn (“Nick & Norah’s Infinite Playlist”). “Two Boys Kissing” reveals his command of an intriguing, complex narrative with an unusual point of view: the first-person plural. This “we” is the combined voice of men who died during the AIDS pandemic several decades ago. As the boys’ stories become more closely entwined and connect in a satisfying finale, the reflections of these “shadow uncles” lend a quality of retrospection that is rare (and refreshing) in YA literature. The “shadow uncles” also tie together past and future, living and dead, and give thematic weight to the novel’s form, with its separate stories stitched into a larger whole, like the AIDS Memorial Quilt, begun in 1987 and still being created.