He really needs to get back out there but at this point it is going to have to be baby steps. He won't be able to add too much to his life because he won't have the energy to keep it up but there is hope. If he can re-activate some of his interests like hobbies or friends and such it would help. Maybe talk to some of his friends and ask them to stop by some time. Let them know not to stay long unless he really wants them to.
I know exactly how he feels.....but, I didn't give up on myself, I made it through it, and I do it by staying clean, taking my perscribed medication, and having found my passion, which is the treadmill, I excercise everyday. Don't give up on your son, show him encouragment, and suggest new and different ideas with him.....I wish you and your son the best.....