You mentioned "future divorce"...and this is my opinion and my opinion only so take it for what it's worth I would be freaking out if this were happening to me....that tingling nervous feeling in your bones, listen to it, this IS happening and those bad intentions you think and feel they have ARE true. I know it just reading the story.
So if it were me I would put my child absolutely first and initiate the divorce...why? In my state (and many if not all other states which you know since you are a lawyer) once the divorce is initiated neither parent can take the child out of state without the first parent's permission. So I would initiate proceedings, rescind permission for your child to be out of state, and pick up child now. If they gave me a hard time I'd call the police in...once the child was safely back in my state I would exercise that law should the other parent take the child out of state without my permission...law enforcement takes that very seriously.
I don't know your entire situation and I realize it's hard to break off a relationship but you could always get remarried later or back together later should she actually rehab successfully .
Just my opinion take it or leave it.
PS - It is hard to find childcare and maybe the first daycare you find won't be that great but it could be temporary while you find a better one. Your story has my fight or flight senses on high alert for you...the worst action would be to none (leaving him in the other state). Again just my two cents.