Thank you everyone for all your posts and the great info. I'm learning so much and it definitely makes it feel less daunting to know I'm not alone. My MIL definitely isn't responsible for our situation but she does add a lot of stress to it. She's employed now and could move out but my AH has her convinced that he needs her to be here because if he were alone with me here, he'd get worse. Total BS. He even sent me some point-by-point characterization trying to shoehorn me into the role of abuser. The reasoning was just so bizarre.
This morning he was mostly himself and acted as if nothing had happened. That's the closest I ever get to an apology because if he felt truly justified and angry I'd be getting the brush off right now. Since he got that out of the way, it's back to drinking.
I appreciate all the feedback and I'm definitely going through all the suggestions here and formulating a plan. I'm sure more questions will come up but it's good to know I have somewhere to turn for answers.