truthfully, I fuck things up all the time dealing with girls. no where near as much as you did. she's basically moved on dude and it will take a miracle for the two of you to get back together again. there's a chance that you might be able to work out being friends. its probably pretty small after you beat up her bf, but there's a chance. It will take time for her to forgive you. everything in relationships is based on time. you're just gonna have to wait it out, or, you can take some drastic risk and hope that you don't fuck things up more then you already have. you're best bet would be to not try to get between the two of them