I think what you're describing is a form of "survivor's guilt." Why him? Why not you?
Who knows, maybe there is no "why." What I do know is that it's bad enough when tragedy or misfortune strikes one person, and the suffering of the victim isn't eased by someone else's suffering. Your unhappiness doesn't do a thing to alleviate his.
Your life is a gift--enjoy it and appreciate it. Sooner or later you'll have misfortunes of your own--maybe not exactly the same kind, but something that makes you unhappy for a while. Enjoy life when it's good.