I'm curious so does mc have a mental illness?

not really, he's just heartbroken, he woke after 5 years of being in a coma and now his boyfriend (or ex) is now dating another guy and its just hurting him a lot and cant seem to let him go

The more he uses his brain, the more his brain will recover. That's all it takes as long as he hasn't received any real brain damage, which I'm guessing he hasn't.