Thinks he doesnt' need friends? Sprialing downward FAST!?

have a guy friend who is involved in an affair with a married neighbor. He vanished for awhile and we have recently begun talking again. In a conversation of the other evening he told me that he deleted a s/n with over 300 friends on it (i new this already...makes me sad), and that he feels he doesnt' need any friends. As we went on to the conversation I hear that he really can't be out of his house for long periods of time as his kids tell "her' everything. My initial reaction is WOW. I really feel bad for him.....it's obivious he's in a controlling situation, and that there is nothing I can do about it except sit back and watch. It saddens me that he feels he doesn't need friends cause when my days were darkest...i got through it with some of my now closest friends. Of course i'm stubborn enough to hang in there cause I know that eventually he'll hit rock bottom. Am I wise in doing this? What can I say to him to help him out of this?