Anne: You are not being childish in this situation. And I’m sure you aren’t alone, either. My advice is to examine your whole relationship, not just what happened on one night. Has your boyfriend ever given you cause to doubt him before? If he’s been good and faithful other than that one evening, then I think there’s reason enough to give him the benefit of the doubt. But I’d let him know that drinking is not an excuse to behave as though there are no consequences.
As for your friend, I guess the same is true. Has she ever given you cause to distrust her? If not, and since she’s a good friend, maybe you should give her another chance. Everyone has said or done things they regret after mixing good times with alcohol—maybe even you have. So examine your heart and see if you can’t find something to save out of this mess.
Now as for the woman, if she isn’t a really good friend, find people to hang out with who have your best interests more at heart. But if she is a valued part of your life, I might cut her some slack. There are lots of bottom-feeders in the fish pond but only a few really good girlfriends.