The Adults by Amy Espach

This book is Emily, aged 14 up to her late 20's and the relationship she has with a man over that period of time. There is a lot more to her story than just one guy, of course. Her parents divorce, she makes and loses friends, her father moves out of the country and in with another woman, having fathered a half-sister with yet another woman. It is not the fairy book childhood. But the realtionship that defines her life is one with her high school teacher, Johannes--who she calls Mr. Basketball. She begins sleeping with him when she is 15 years old, and she does so ardently, enthusiastically, and the teacher loves he back, no question about it. He is not just bedding an underaged girl, he is falling hard for her. Why? Well, he is one of those men who is not much more than a teen himself, in maturity if not age. He is 24 when the affair begins, and he still doesn't have sheets on his bed--it is like he was orphaned too early to learn the ecoutrements of a civilized life--like how to make your bed and cook your dinner.
The two meet up several times over Emily's subsequent life--she move on from Mr. Basketball, but when he shows back up, she is her 15 year old self again. Just a horny as before and unable to stop herself from literally jumping his bones. it is a story about how those first loves are intense loves--maybe not all that good for you, but very intense. And they don't fade away--those memory tracks about how you felt when you were with that person are hard to stamp out and intensely written. Be careful. That is how the story goes.