It’s been almost a year since I first heard the term “New Adult,” in association with Tammara Webber’s book Easy. The genre has exploded since then, and I couldn’t be happier about it.

To be honest, my debut NA novel, Where I End and You Begin, has been sitting in my brain, percolating, since 2009. I tried several times to write it as a Young Adult novel, but the strictures of the genre kept hampering me—things like dancing around the topic of sex, or drugs, or alcohol, the problems of what to...