Being drunk is no excuse for your actions. People love to use it as an excuse, especially college-age girls who pass themselves around campus. Well, the story would be different if one person used the alcohol to take advantage.. but I've seen girls basically throw themselves on sometimes unwilling dudes at parties.
Anyway, friendship does lack formal commitment, but it's not always one sided.. It's one of those take-it-or-leave-it situations I guess, and that is probably how you have to deal with events within a friendship. Things that break up friendships are things one person can't really take.. whether it's violent tendancies, conflicting tastes for food, selfishness, adultery, or pet peeves.