Harry Potter and the Prisoner of Azkaban
Aside from a hint at a few crushes (Ron on Hermione, Ginny on Harry, Harry on Cho) we get practically no romance. This stands to reason, though, since this novel focuses on good old pubescent thirteen-year-olds, after all. It's notable that these kids are ushered into the adult world via war, death, violence, and crime rather than sex. If you want some romantic action, you'll have to read the later books in the Harry Potter series.