I think you 37 year old son needs to grow up. If he has a mental illness, he needs to accept that and adapt accordingly. Letting him experience his imaginary world in your attic will not bring him to "our" reality. It might be what he says he wants, but I doubt it is in his best interest. What will happen if you die, or for whatever reason you can't support him, what would happen to him then? Do you really think anyone but you would tolerate this?

I think you need a plan and you should talk to a professional mental health worker for advice on what to do. I think your 37 year old son is in a bad state of mind, maybe he is embarrased of this. That might be why he hides from everyone.

G'luck. brook.