It disgusts me to think that your flesh and blood brother and his wife would break a very important rule in your house. I can only imagine your emphasis on that rule given your husband's history with alcohol. Were you upset with them as well??
An alcoholic lives day to day resisting that temptation. I'm not saying that your husband has no power in this situation, he certainly does! What I'm stating is that alcohol to him is like a child in a candystore. Sure, you can tell them to look but don't touch....but how many of us ever followed that rule growing up??
What your husband did is WRONG. He may very well not remember the whole sex ordeal. Alcoholics do tend to black out and not remember anything while being drunk. That is not an excuse! He did what he did, and he has apparently apologized for it over and over again. Now, I think the right thing for him to do is to show you he's sorry by truly avoiding alcohol. Remember, you have children involved in this, so keep in mind what YOUR breaking point is. When is enough enough?
You can beat a dead horse, but what good will it do? I'm not saying what he did is right, I'm merely suggesting that we view options to address the issues now, which are: loss of trust, depression, and a sense of chaos.
Loss of trust is something that should be rebuilt given enough time. Give him a chance to prove himself. Let's face it, your trust wasn't built over night, nor in a matter of minutes.
I would also address an anger you should have with your brother and his wife. How dare they bring alchohol in your house when it was clearly a rule that they shouldn't do so in the first place!
It sounds as if you're depressed. Certainly this situation could add to this depression. If it just came on as soon as this whole ordeal happened, then I would suggest trying to resolve the emotional issues surrounding your husband. I have a feeling that when you resolve that then the depression may start fading. If not, then please see a professional!!!
Do NOT try to bring another baby into this right now. You are right by not wanting to. You need to resolve the issues at hand and then you can move on from there.
Lastly, if you choose to leave your husband, you are not LOCKED in. You can find a job (seems as though the economy is turning around.) Never feel like you don't have any other option than to stay in an unhappy marriage. I'm a big advocate for staying married, but if you're truly unhappy and he hasn't changed, then by all means get out of it.
My advice is just an opinion on what I would do if I were in your situation. I wish you the best and hope that you come to some understanding as to what you should do. Best of luck!