“I feel I will fuck him up completely if I leave.”

No, listen: he will f*** himself up completely when he drives you away. His actions, his responsibility.

He is not your son. He is a grown man, responsible for his own choices and his own happiness. It’s not your responsibility to keep him afloat. He seems pretty determined to be miserable anyway, so there’s little you can do to help.

For your own sake, and your sons, you should go. You can’t hang around just because he feels he needs a punching bag – an emotional or a literal one. It’s going to be hard as hell but start taking the steps: talk to people who are on your side, family, friends, colleagues. Work out what needs to happen for a physical separation. Talk the plan over with your allies, and then do it.