As Andres said. She is being selfish, and abusing your trust and emotions. Please, for your own sake do not go back to her. Yes, it's nice to think about helping people out, but in a situation like this where you now have very little to do with her you should think of yourself first.

On the other issue, 15 seems a little young. You are 18 correct well, 18 /2 = 9 + 7 = 16, which is sort of downward limit. However, I'm not here to judge and at the end of the day you should do what feels right by you.