I've been where you are. I stayed and things only got worse. I was pretty broken down by the time I was able to leave. If you have the resources in place, and it's an option, wait until you have a window of time where he is gone and get yourself and your son out. This man is dangerous and will not get better. Alcohol and drugs are only part of the problem. My first husband rarely drank but was a compulsive liar and very controlling and abusive. I left him while he was at work. I knew he had an unregistered handgun in the house and I took that when I left and threw it in a garbage can at the first rest stop we stopped at.
I'm not advocating that, but it made me feel safer. He flipped out about that gun, but there was nothing he could do. I told him he should call the police and report it stolen. He didn't.
Then after I left him I got involved with and alcoholic who started out fine, but degenerated to the level it sounds like your husband is at. Ranting, raving, name-calling, verbal and physical abuse.
I left him too. Last September. He made a lot of noise about custody and stuff, but the truth is he can hardly take care of himself and so all his big talk was just quacking. He's busy drinking and feeling sorry for himself and I'm busy building a life for myself and my sons. My ex husband died of cancer last July and I was so relieved. My oldest son is in grief counseling and doing well, though he misses his dad. I never say a bad word about him. I can afford to be charitable now that he's gone, but his death is still on my gratitude lists.