As dollydo mentions, you have options. You can stay there, ask him to leave, and take on a roommate (perhaps another mama who needs someone to share childcare with). Or you can move in with your parents.
I chose option B when I left: my exah and I had a civil discussion regarding separation and then, one day, he started to threaten me and demand custody of our child, telling me he wouldn't *let* me leave. I had already been packing but at that point, I freaked out, called my parents, and they moved me out of there in less than 90 minutes. I took clothing, a rocking chair, a mattress, and toys for my little one. Everything else got left behind, and I was GLAD for it.
Living with my parents has given me the opportunity to get back on my feet financially and emotionally. I paid back *all* the debts my exah put in my name; I have saved money and I'm two years away from purging my bankruptcy from my record. It has given me a safe place far enough away from him. My daughter has blossomed when she was taken out of that toxic place...and when he stopped seeing her because he was pig-headed, things got even better. My little one started smiling again...and I remembered what it's like to be happy.
I understand your reluctance. It's part of the grieving process. You are grieving that dream you built for your family, and it's entirely normal to fight anything that you feel will take you away from that. Let me offer a different perspective: just because you leave doesn't mean that at some point in the future, if your spouse finds recovery and sticks to it, that you could not resume your relationship again. If it's meant to happen, it'll happen.
(As an aside here: when I left my then-husband, we had JUST moved into a new apartment and purchased a whole new set of furniture as per his specification. I fought with myself endlessly to justify staying because of all the money I'd spent...but looking back, HP was giving me a big red sign saying: "This isn't working anymore!!").
As for being the bad guy in his eyes...there's really nothing you can do to change or control his opinion of you. Yes, there will no doubt be backlash, but in the end, your leaving would be just *one* of the consequences of your AH's choices. You cannot protect him from those consequences. He's a big boy and he will have to deal with them himself.
Keep posting!