CoffeeLover, I completely understand how you feel. There's nothing wrong with taking care of yourself and letting him get baptized without you there. It might be best that you are not there. The church will have plenty of people to support and encourage him. Maybe there will be some recovering alcoholics who will step up an encourage him and share their story with him. It sounds like he's going from one extreme to the other when all you want or need is just to breathe and have some calm without every moment being an emotional roller coaster. I understand that as my husband put me in similar situations regarding church. We were always on the pew on Sunday morning and then he was drunk on Monday.
Please do not be pressured into doing something you do not feel comfortable doing.