Hi AL, as Sparklekitty mentioned - it really is that bad.
So how can you prepare yourself? By seriously looking at the situation and taking some distance. If at all possible can you go away for a week or two? Go visit your family or rent an AirBnB somewhere, just let your ABF know you and your child are going for a get away, a change of scenery. Chances are he won't care based on how he is behaving.
This gives you time, away, to really see what's going on and to clear the FOG (fear, obligation, guilt).
I am of course worried financially but also that I need him, for I don’t know what!
Well, he wasn't always like this was he. This is not what you were expecting. It may not have been a fairytale, but probably had many good times. You probably expected that to continue (that's not unreasonable). But alcoholism is progressive and maybe having the extra responsibility of caring for a child was just too much for him as well.
Financially, perhaps Monday would be a good time to get on the phone with the domestic violence people, as dandylion mentioned. Take action, it will make you feel SO much better. There are probably tons of resources out there that you aren't even aware of.