It sounds like he has a really serious depression, perhaps even psychotic if he's waiting for the "**** to hit the fan". And as you say, he's paradoxically intensely focussed, and drifting. If he could get better that same determination would really steer him well... I think you're right that you have to see a doctor about his problems.

I'm a mother myself, and I really feel for you. I would be heart broken if my son was suffering as much as yours. And no, it's not your fault.