Teenager girls are hard!!!

Being a parent is never an easy thing. My 16 year old has a very controlling boyfriend that has changed everything about her. Thr2type of music she listens to the clothes she wears and even who she hangs out with. I told her she was no longer allowed to talk to him because I feel he has too many issues and is not good for her. She then cut her wrist and is giving me all kinds of issues. Does anyone have any advice on how to help her get over him?