We all make mistakes. But there are just some mistakes that a relationship can't survive. For me, this would be one. I'd get rid of the chick for sure and tell her she needs to start attending AA meetings. I hate people that use alcohol as an excuse to be assholes. I saw an episode of Cheaters where the guy's twin brother was the one cheating with his girlfriend. That has to be one of the most difficult things to deal with: a bout of infidelity that involves a sibling. Your relationship with your brother will no doubt be changed forever. You'll never look at him the same. It will be extremely difficult for you two to heal the bond. But if you both want that, it can happen. Not too sure what to do about that buddy. It all depends on how you and your brother's relationship proceeds. Good luck with that man.