I have a friend who has to fight a running battle with depression. When she's having a really bad time, it makes my life a kind of hell, too. But what's worked has been persistence. I just keep being there. I send balloons sometimes. I make sure she eats something.

What I haven't been able to do is get her to go to a physician for a thorough physical. (No insurance.) She has allergies (which can be severe), TMJ, and other symptoms that mean that she spends a good deal of her day in pain. My own depressive fits are strongly tied to my physical well-being, and I'm pretty sure that she's worst off mentally when she's bad off physically. (_I_ notice the pain lines on her face and suggest tylenol before she notices that she's hurting.)

If you don't want to buy the books on the 'net, go borrow them from your local library. Read widely. Read people who disagree with each other. It makes a difference to your well being when you can recognize that your friend is rejecting your company because they feel unworthy of being loved and not because you're an awful person.

You might want to investigate bioneurofeedback. I have no personal experience with it, but I've heard good reports from some fellow librarians.