It's been quite a few years since I read this but from what I remember it was a coming of age story where the main character was helping his cousin (although it may have been an aunt who was the same age/younger). She was visiting and wanted to have her first time. He agrees to help coach her to hook up with a friend of his at a party that was coming up. Long story short he ends up with her despite having a lot of reluctance to her advances. She was described as being a bit extra or wild I believe.
This is what I remember at least, been a while and I've had no luck searching for it multiple times over the last couple years.