Two years is a pretty long time to get over someone, so there may be some other factors going on with your friend and his emotions. His depression may have started with his former girlfriend but be tied to other issues that are still going on in his life now. Or maybe the relationship stirred up other issues that are making him unhappy two years later.

It sounds like you've talked to your friend about his issues (since you know about his last relationship), but if you haven't, consider asking him how he's been doing and how you can help him if he wants to be helped. Sometimes people need to work out issues on their own, and if that's the case, he should be able to tell you that.

But if he feels like nothing is getting better, or if you feel that he can't handle his emotions on his own, he may need some professional help. Talking to a therapist, school counselor or psychiatrist might benefit him immediately. Also, some clinical depressions are based on chemical imbalances that can be helped with proper medication.

Let your friend know that there's nothing wrong with getting help--whether from you or someone else--if that's what it will take for him to feel better about things. Also, supporting your friend by listening to him, pointing out other things that are good about his life and being social with him will probably help him realize that things can get better.

However, friendship should work both ways, so make sure that your friend is as supportive of you as you are of him. If it gets to the point where your friend is refusing any help, won't consider seeing a professional or insists that he doesn't want to change, you may want to reconsider the friendship altogether.