Addressing miserableness in a colleague

I work with an unhappy misanthrope.

He is smart, and would be good at his work if he could pull himself out of his state of perpetual ennui. However I think he may be depressed, and he doesn't seem to be getting any better. I am aware that various senior management types have been "working" with him and there have been some baby steps, but his general demeanour is still that of a man who would rather rip out his fingernails than spend more time than is necessary with his colleagues or deal with the parts of his role he doesn't like.

I have known this man for many years, and working with him closely from time to time. We are both in demanding jobs, where we are required to work long hours and must be able to attend to tasks with a high degree of precision. He has very good skills in some areas, but his unhappiness spills into his dealings with others, his reluctance to do the routine mundane parts of the job and his sense of professionalism. After a while others have started to avoid him, and a poisonous and pessimistic aura is now attached to his name. He lives by himself, and with no one to talk to at work I think he is really lonely.

Is it wrong of me not to want to get more involved and try to help him out? I quite like him and I feel like I should do something, but part of me holds back and for mostly selfish reasons: I don't have enough time (particularly as he likes to have very long conversations about how miserable life is), others are dealing with it, he won't improve, it is not really my business, I should focus on the young ambitious and overworked women in my team etc ....

So you see I feel terribly guilty about this and think I should do something, especially when I see him wandering around in an obvious state of despair looking for someone to talk to/at. On the other hand I'm at a loss as to what I can do to help, other than to refer him to the support that is supposedly already available to him.

This one needs more thought.