I just spent 2 years talking a friend of mine down. He was in a simular situation with someone in his karate dojo. It took two years for him to work through all the emotions, the sense of betrayal that his sensei did nothing to stop the situation and other factors. last night he finaly got up the courage to walk back into the dojo and try to settle the situation but ONLY because the other person involved has moved out of the area and would no longer be there.
Sometimes it's eaiser to face a situation as soon as it happens, get it over with and move on.
But sometimes you have to take a step back and get yourself back to center before you can face the situation.
you didn't just get into a fight Andrew, you got into a fight defending the honor of someone you care about and from the sounds of it you're feeling somewhat guilty as well. You need to go back and deal with the guy but you need to deal with YOU first. If you're still kicking yourself, stop. If you're still mentaly kicking the other guy, stop. If you're mentaly kicking the girl for getting drunk (and kicking yourself for being upset since she didn't know better), stop. Take a deep breath, let it go, get yourself back to emotional center then walk back into the dojo and deal calmly with everyone involved.