I read plenty of adult and young adult depending on if it something I think I'm going to like, and this sounds YA to me.  I've read plenty of YA books recently that explore similar themes, such as the main character losing her virginity and learning to use some type of powers she's developing.  I think the line gets crossed when a writer goes into too much specific detail about sex.  YA  generally uses abstract imagery to describe sex or skips the actual description of the act altogether, only using the barest of detail.  For example, Bella and Edward's honeymoon in BREAKING DAWN or Seth performing oral sex on Aislinn in WICKED LOVELY.  You could look over those as examples of where to draw the line between YA and Adult.  I hope this helps.

Melissa Southern