Yes it is hard to leave an abusive relationship - Ive been there - but you've posted a couple of times before, haven't you? & yet you keep backtracking. Even in the face of all the good advice you've been given on MN. Not even the fact that your DS left home because of this man, your DM doesn't visit (she probably can't stand this man and the fact you won't leave) can sway you. You even speak as if its impossible for you to have friends, work, retrain etc..errmm...all for the sake of 1 man? You weren't born with him. You existed without him and you can again. You aren't living in a back of beyond, remote country.
I don't know what the answer is - but its not coming here to vent every so often then going back to an abuser who is messing up yours and your DCs lives. The man has spat in your face - how filthy is that...could you let him touch you, after that?
You will lose your children - they won't stay young forever and will run a mile away from you and this loser as soon as they can. Then all you'll have is him, and your bitter regrets over the years you've absolutely wasted on this man, when you could have long ago said "no more" and done all in your power to remove him from your life.
You said he won't give you a break for a minute, when he's at home. The man sounds like a bloody pest. What makes you think you can't survive without his company?! What exactly do you need a bully in your home for? If you want company there are loads of groups and meetups you can join. I simply can't fathom why this pig has become your world.
What about your son, and how he feels, what he is hearing and witnessing? The resentment that must be building up inside him? Does that count for anything? Its actually upsetting to read.
I hope this time you actually heed advice and call Womens Aid.