Sounds like BPD. She has BPD.
Check old threads here on borderline personality disorder. There is a large amount of them with good information.
You basically have a few options, but nothing will make things normal. Your only option is to end this. However, you must do this carefully not to fuel a BPD rage.
Listen, kid...I'm not here to play games or sugar coat things. YOU end this now. It will not get better. You explain to her it is you and not her. You do this gently and you do it right away. No matter what happens, you do not go back for sex. She will try bringing you back in this way.
She will find someone else quick (the BPD's do), but she will still want you. If you can stay away, her grasp on her new one will stay tight. She will move on.
I've seen this too often and I've seen a lives ruined. Stay confident and stay strong. Do not let this define you. You will find much better.
Has she hit you at all? Open or closed fist?