Jamie, I understand how you feel. I just posted a post a couple of days ago about my sister who is similiar to your member of your family. See post if you like: http://www.mamapedia.com/questions/12490715560616787969
Maybe there is something there from the responses and from what I said that could be of help.
People like that tend to thrive on their misery and that's all they can focus on. It really wears on those who have to listen to them. I have tried to tell my sister, who is always complaining about having difficulty making friends, that if you are always negative, of course you are going to have issues. People gravitate towards positivity. Dealing with someone who is always so negative, someone who is very needy, etc, is a lot of work. And to top it off, when we need to vent, they have a difficult time just listening, more times than not, they'll switch it to something they are dealing with, like they are trying to top what you said.
All I can say, is limit your contact as much as you can. If he starts to complain, you can turn it around on him and say, well what are you going to do about it? Or be like Dr. Phil, "How's that working for you?" OR you can say oh I'm sorry, and change the subject. OR you can confront him about it. Do it in a nice sensitive way. Like, "I understand that you are having issues with.......and I would be more than happy to help you set up a plan of action if you are going to agree to follow it. But if not, I wish you all the luck then with it, but I'm sorry, there's nothing more that I can say about it." OR "I'm really sorry you are going through this but I don't think I can be of any help to you with this. I am too close to the situation and am afraid that I will be unable to be objective so I think it would be a good idea that maybe you see a therapist or someone else. Maybe they can advice you as what the best option for you would be." I'm planning on doing this with my sister the next time she goes off on of her many woes.
It's not easy I know but you need to protect your peace of mind. Good luck. Sorry for the length. This is obviously something that is close to my heart right now.