Though there are no explicit sex scenes in the book, it still takes place at a high school where a bunch of teenagers are away from their parents. There's obviously some exploration going on. Frankie is just a sophomore, and she feels uncomfortable being too sexual with her new boyfriend. But she does wonder about whether it bothers him that they only make-out.
And there's also a fair amount of speculation about the other characters. For example, Frankie often wonders about Alpha's relationship with Elizabeth. After all, they're both seniors and Alpha is so testosterone-loaded that it makes sense that they're probably having sex. When Alpha makes a comment about his sensual body after coming back from the yoga retreat, Frankie thinks that he must be having sex and wonders again if Matthew is disappointed in her.
We get a glimpse into Frankie's innermost thoughts as she tries to navigate the waters of high school sexuality… and what she's okay with doing.