Don't let him blame it on the alcohol. That's just too weak.

Do not take his calls for 3 weeks so you can think, if after 3 weeks he has suffered and is still trying to reach you, allow him back in little by little because if you just take him back it might happen again. And drunk is not an excuse unless he's never going to drink again! Men do it to girls when they don't even like them, he has to remove himself from temptation to regain your trust, just make sure you call the shots, not him

okay 3 weeks and only when he was drunk? Was he drunk for 3 weeks? No matter how hoey this girl is, she is not the one to blame your BF is. Don't fall for blaming her and letting him off the hook. I don't now if you should take him back, that is your decision, you know your relationship and know whether you can build trust with him again, I don't/

But I do know that its too easy to blame the other woman and let him off the hook for his actions.

Did he actually sleep with her? Or was it a drunk kiss? Ether way he should of had the responsibilty to not cheat. A kiss is easier to forgive and understand because it could have happened forceful on her part. If he slept with her, thats kinda a different story, im sure most people have the sense even when they are drunk to not sleep with someone else if they are in a committed relationship, it sounds like he wanted to give it a try then use the "I was drunk" excuse to possibly get away with it. Its ultimately up to you, but if he slept with her I would drop him, if it was a kiss, id give him another chance.

Hope i helped.