Kate, I hate to say this, but your husband sounds like a mama's boy, and nothing is going to work if he doesn't put you before his mother.
From your description, he puts his work first, his mother second, and you and your son dead last. That is a bad prescription for a marriage.
Perhaps what you two really need to do is separate so that he understands what life is like without anyone at home.
Have you seen an attorney? You need to. You need your own bank account and credit cards. You need copies of tax returns, bank statements, brokerage statements, your husbands benefits package at work, the whole thing. And you need to put money in that bank account before you separate. The attorney needs to make sure that he cannot drop you and the baby off the medical insurance too.
If he doesn't start changing his attitude, there will be nothing left for you to do but tell him to leave. Get that lawyer. Keep going to counseling. But protect yourself.
It's too bad your MIL doesn't understand that she will slit her own throat on this. She won't see her grandson nearly as much when you two aren't married anymore. What a twit!
Dawn