Yeah he sounds depressed. I have two brothers, both of whom have behaved in similar ways to this man, but one has Aspergers and the other is bipolar. My brother who has bipolar did this in his depressive states; wouldn't leave his room, had destructive girlfriends, couldn't get along at work, worked low level jobs... Once we found out what it was, he went to therapy and received medication and got a lot better. He no longer is the dark cloud growling around the house (most of the time). Also, his bipolar symptoms began around 14-15 yrs old. It was the same year he dyed his hair black (half style statement, half how he must have felt).
Both my brothers have received therapy, so I think it's crucial that he sees a professional. He doesn't have to take medication, just talk to someone who knows what they are doing. Also, if his sister can ask him personally how he feels about his life, he might tell her something enlightening. I'm not sure that the parents will be much help though...they don't sound too interested.