I can recognize the part of the cycle your husband is in. The first time I quit drinking I was sober for eight months. It was really hard but I did it and without much external help or really losing much in my life. So even though I'd heard all the horror stories, I couldn't understand that I could still be addicted. How could I possibly be if I could go so long without a drink? I understood that I couldn't drink all the time, but why not just on special occasions?
So I started drinking again, and it was fine at first. Just at a wedding, then a few weeks later at a birthday, etc. But it got worse, and worse, and worse. A year and a half later I had completely destroyed my career, my health, and my personal life. I quit again (not easily — I had to go to rehab and I'm still in the process of rebuilding my life 10 months later). This time I understand, on every level of my mind and body, that I can't drink normally. That my brain is different from other people's and no amount of good behavior will ever make me able to drink.
That second part... the totally ruin everything so that you finally learn part... took me a year and a half. That's a long time. It takes some people even longer, decades even, to get clean again. (I was very lucky, very very lucky, even though I lost so much). There's really no way of knowing how long it will take your husband to realize that he can't drink, or if he'll realize it. And based on your story I don't think he can. I know it's awful but right now the only thing you can do is let him take his journey and do everything you can to protect yourself and your child from the fall out.