There's this guy that I know and I really like him but he doesn't like me. But he told me he's really depressed but won't tell me why. What should I do?

There isn't much you can do. The only thing would be to suggest he see his doctor about his depression.

He opened up to me a little but he's still really depressed.  I want to help.  I'm one of his only friends.  How do I make him feel comfortable talking to me