I totally understand. On one hand it's easy to think it's just money - happiness and staying sane is more important but realistically the financial side makes it difficult to break away and start afresh, especially as you've worked so hard and been through so much to get to this point.
I feel hypocritical giving advice as I haven't got to your stage yet but I think you know that you need to leave its just a matter of when. It might be worth you working out how soon you can both get the debts paid off and know you'll leave him then. Splitting up but still living together would make it so much harder and his behaviour might get worse towards you. I'm not sure if it sounds callous to do it this way but it's both of your debt and I think you'll feel happier knowing that there is an end to the pain in sight.
Like me you might have got to the stage whereby you realise that you don't love him anymore and everything you are trying isn't working. Things will never change until he admits he's got a problem and deals with his issues, that's not up to you anymore. You have to do what's best for you and your son.
You sound like you are in a great place with work so stay focused, make that secret plan, knuckle down and save whatever you can and it will keep you sane until you can leave.
I find that books and CBT (through NHS after speaking to my doctor) is helping me through.
I have no idea if what I'm saying is the right thing for you but I do know that we can only tolerate so much before we crack. A life treading on eggshells is no life at all. You are switched on and strong and you will be ok. You so deserve to be happy. One day you'll be able to sit on a sofa laughing with someone out there who will treat you respectfully and lovingly, as you deserve.