How do you break up with a crazy girlfriend she keeps telling you she would kill herself if you do it you dont know what to do?

OK firstly its important to remember that you mustn't stay with her because of this. Essentially she is blackmailing you into staying with her and that's always wrong. Its clear that she needs professional help. The best thing to do would either be to speak to someone who can help her or to talk to her about getting professional help. If you really don't want to do this you need to at least try to tell her parents or someone who you trust will be able to help you. If you feel very bad about leaving her you could tell her that you want to be friends and help her through this. It might be a good idea if you stopped dating her as its clear she can't deal with the emotional strain. Overall you must remember that its not your fault and that you don't have to stay with her.