Does your son have a job? CAn he manage to stay on his own, or share an apartment with a friend?
If he does, I would do everything possible to get him out of the house. He'll get use to being on his own. It just takes some push that first step. And you will feel guilt, pain, and heartache, but once he's out he'll find his way. Believe me, he will. Then you will feel GREAT!
It's just that first push out of the house that's the hardest.
Of course if he don't have a job, nor anyplace to go, I can understand why he'd be scared and you also.