What do I do for my depressed fiance?

We have been dating for 3 years. He has always been prone to feeling down (never anything that would suggest depression) and been a bit of a pessimist. About a year ago, he took a job in a different city while I was still in college. Since then, he has been having worse and worse episodes of depression. At first I thought that it was the stress of a job that requires him to keep strange hours and travel a lot or maybe the stress of moving back in with his dad, who he doesn't always get along with. But now it's worse than ever. After doing some research, it appears that he may have dysthymia, a form of depression. I confronted him with my suspicions and a list of symptoms. He agrees that this seems likely, but does not seem to see any point in perusing treatment. He does a lot better when I visit, but I live two hours away and cannot see him more than a couple times a month. I have found some treatments that to try at home (he does not have the money to see a therapist at this time), but he just can't see the point of trying and really believes that things cannot get better. I do not have any illusions that I can "fix" him, but how do help him to get motivated to help himself, especially when I don't see him very often?