Advice?

My ex-boyfriend (21) has been chronically depressed for a long time. His family are extremely homophobic. His friends have drifted away. He is now off away at school, in his junior year of college, and he is as lonely and isolated as he has ever been. He is also far away from me, now, and I don't know what I can do to help him.I (24) am at a loss. I have tried everything I know how to do to make him feel better. He tells me he's a failure at life, that he is tired of never measuring up, and he has become the most self-critical person I have ever known. It's gotten worse since we broke up.I broke up with him because I was convinced that we were not going to work; we are just better as friends than as boyfriends, because even though we have a lot in common we never were romantically compatible. He wants (not sexual, but emotional and familial) things I just can't give, and that I never want for myself (don't want to elaborate on that here, sorry).Worst of all, even though he won't admit it, he compares himself to me... which is seriously causing a lot of problems because he feels like if he doesn't measure up to me, then he's a failure. This is the same thing with the general public.I have tried to get him to talk to someone. I have listened. I have consoled. I have given advice, let him vent, put things in perspective. I have been patient and understanding, and I've tried the tough love approach. Now, I'm at a loss, but I will not abandon him... and I need help. He's expressed suicidal thoughts before, and he's doing that now again.What should I do?