Right. That relative is miserable in mind, body or both and probably more than a little jealous.
Relatives are funny. I have found that it is easier to love a stranger and feel for her than many of my relatives. Why? Because strangers at least are polite to me. Relatives tend to be petty, jealous, rude and when they come "visit" me, it is to use my house as a hotel...ie, not for the purpose of visiting me. At one time, I was expected to drop whatever I was doing, to lend an ear and become a free psychologist and listen to these deranged people without saying anything "negative"'. However, whenever I had a problem, they would either not want to hear it because something more important was about to happen OR it would be laced with "I told you so" and negativity.
The best thing is to ignore and no longer actively include these life draining leeches in your life.
If you can't ignore and you're still hounded, draw the line.....Give him/her something to read..... how about a story featuring this particular relative, to be plastered all over cyberspace?