Honestly I think you would benefit by seeing a Therapist ( I’m not sure you might already ) to process things.

I’d file for divorce. I’m not sure if you own property together of course that can take a bit longer to separate financially waiting for it to sell.

But if your really wanting to stay and “hope” he stays sober and clean and not become abusive again and I say “ hope” because honestly you can’t help him” he has to want it.

I absolutely would not bring a child into this marriage. Until he has at least a couple years of him being clean and sober 100%

And I’d block his Mom on Facebook who needs her drama??? No one

I’m sorry about your brother I hope he’s able to stay safe.