I ABSOLUTELY COMPLETELY agree with what Hammer said. VERY sensible, very well put. So, in following that line of thought, here is my opinion and I am in a bitchy mood today so it isn't nice.
You have just gone through this massive paradigm shift, your life has totally changed and suddenly you are the sole support of yourself and your children. You should not be "pressured" with any thoughts of having to take care of a grown man who is clearly an alcoholic with who knows what other issues. You should not be "worried" about taking care of him and his mess....take care of you and the kids. Period. To hell with what HIS mother says, if she is anything like my ex MIL then her boy can do no wrong, and therefore, let HER deal with him and his chaos. Seems to me he "abandoned" you when he picked up the bottle and got addicted, and don't put yourself through all the guilt, etc, it is not a crime to protect oneself and children in times of family crisis. Get a lawyer, get yourself your own bank acct, etc. This is the time to buckle down and protect you and the kids. Stop feeling guilty about it. Do NOT let people tell you how to manage your home or your kids, or your marriage. If you cannot be married, or do not want to be married, then that man is no longer your problem, so to hell with whoever is berating you. Tell them to shove it in their donkeyhole and go no contact with them. All that matters right now is your welfare and your kids welfare. Like I said, I am not Miss Sunshine today, I am sick of these alcoholics destroying good people's lives. Focus on you and your kids. Get your house in order. That is what I am working on. Your kids deserve the best life you can give them, and this is your first step in that direction.