Honestly, tell your buddy's parents or something.
Obviously somebody who has more power of your friend needs to do something about it.
Depression is a very serious problem, take it from me, somebody who has suffered from depression for many years of their lives...
Don't spoil your friend, and don't do everything he wants you to do, make sure you treat him no different than anybody else just because of his problems.
Take the time to try and talk to him about it, see if there is anything you can do to help him.
Don't get angry with him during the process though, even if he says something you disagree with or dislike. He is only human, always keep that in mind.
Try and find ways with him to cheer him up, if you can't help him, try and find somebody else who can.
I know that for him it is going to be difficult to have somebody trying to help him, especially if he doesn't want the help. A lot of people can not admit to being as depressed as they truly are.
If you can't help him, try getting somebody else to.
I've learned that one of the keys to happiness is finding your own ways of cheering yourself up, nobody likes being depressed.
Try and get him to do the things he enjoys doing, he will probably have a lack of motivation to do anything, if he doesn't enjoy the things he does or no longer enjoys the things he used to enjoy, try new things with him, make him experience new things throughout his life, and hopefully he will find happiness in one of those things.
Depression is incredibly difficult to maintain and fix.
Don't be surprised if you can not help your friend, but always be there for him, you seem to care, and that's a great start. Don't give up on him, he needs you.
