I lost a friend or was she just using me?

It sounds like you already know that she’s been using you. It may have been intentional, or it may not have, but either way she seems to be a bit violent for a “friend”. I think it would be a good idea to… well, not ‘avoid’ her, but kind of keep some distance. Don’t just give her the cold shoulder, be polite and courteous, but that’s all you need to do. If she really needs people to hang with, and to help her with stuff, she needs to learn how to treat people first. As for cutting… don’t. There isn’t any point. All it does is give you scars–it doesn’t solve the problem. In fact, it adds to it. Instead, find something you can break, or punch, or kick, or something. Scream into a pillow while you do it, if you have to. I hope you’ll find a suitable solution soon!