The problem is you letting her string you along. Are you sure you act your age compared to her? Seems like you act weak.

You can decide if you want to be with her if she is willing to cheat on her BF. If you are, keep seeing her and make sure she knows you want to see her romantically. Just know that if she cheats on her BF, she will cheat on you.

If you don't want to be with a girl that is in a relationship, tell her to contact you once she is available. Then don't contact her. If she contacts you, ask her if she is single. If not, end the conversation politely.

I don't know her being somewhat of a drama queen, her mistreating her BF, and her walking all over you fit in with your '99% compatible' number. You sure you factored all that in? Never mind the age difference, which may create problems, if not be it what others think or how it is secretly something both of you aren't completely comfortable with.

I lost my mind over a 21 year old girl when I was 17. I lost my mind over a 19 year old girl when I was 32. I know what it is. At least in my case, I know they both are/were honest and good for me. With all that you say, I am not so sure about that.