talked some last night still working on this. It is a hard nut to crack.. lol
Ugh. Those adult kids that want to be little children their whole life is annoying, isn't it? Have you ever asked him how he felt about his son's issues (work ethic not being very high, low ambition, etc.)? I mean in a nice way to see if it does indeed bother him. I'm guessing it does but it is hard when it is your kid and he could get defensive. But it is something I'd want to know. If he has no problem with it----------- that would not be good news for his ability to be with you without him. If he feels frustrated but trapped---- that is good for you.
Then you can talk about ideas for how his son can earn a living on his own---- trade school, apprentice, a job he is already qualified for.
But you have to let him kind of come to the conclusion himself with you only quietly leading him there. If you are aggressive about it, he will get defensive.
But I agree, it is time for this man to be able to move on from the supportive (literally) father role. Three and a half years is a long time. So talk to him. good luck