I feel your pain, I'm in a similar situation right now (though in my case, it's my wife who is the alcoholic). I am thankful that I have the support of my parents, and her parents, in caring for and protecting our 4-month-old baby. It's been the hardest thing I've ever done in my life to stop and say "I will do whatever is necessary to protect this baby from harm, whatever the personal cost." That's what's at stake.
What I've learned, and what you already mentioned: if you're going to make a break, have a plan. Don't speak and act out of emotional exhaustion. Get some legal advice, even a free 30-minute free session will do wonders to give you confidence about what your options are. Be honest with yourself with where your line in the sand is, communicate that to him, and be ready to act on your plan the moment he crosses the line.
I haven't acted yet, but we're standing at the line and I can see the tension building inside of her like a tornado. And I'm terrified about what happens next. But I would rather struggle as a single father and give my son a childhood without memories of a drunk mother falling down the stairs.