I’m so sorry OP, this sounds horrifically hard.
In all honesty, given he’s violent and abusive to you, I think I’d be informing him of a deadline when he must change his behaviour, or move out. You don’t have to live with domestic violence - and that is what this is. It’s abuse.
The only thing to be done re the money is hide his post, and given how angry he sounds I don’t think I’d risk that. He’ll find out about it anyway when his friends get theirs and talk about it.
Maybe don’t hide the post exactly, but put it in the kitchen or something where he won’t see it without hunting, but if he comes across it you can just play dumb and say you left it for him to open as it was in his name.
But I’d be telling him he needs to knuckle down and go off to uni, or else get more hours at his job and move out. Do not let him live with you for years treating you like dirt and intimidating you. Being kind won’t help him return to the boy he was; only time - and his own choices - can do that.
It might be worth- if he’ll talk to you - trying to find out why he’s so angry. Did something bad happen to him in childhood? If he won’t talk to you is there a family friend he’d talk to, or would he see a counsellor? If he doesn’t change his ways though I think him leaving is your only choice.