Hi, Catlin!
My experiences are pretty much the same as Truthsayer's. I agree entirely that these people rarely know what they're doing. My view is that they have what I can only describe as an emotional vortex which will suck you in unless you are wary. They have "hooks" to get your attention - usually surfaces as an attempt for the sympathy vote: "look at me, isn't my life awful" and of course you fall for it. Who wouldn't? And yes, they never listen to you or show any real interest in your life. I have come to the conclusion that they home in on what they perceive as another's happiness and, having no means of building it up in themselves, have some sort of belief that they can syphon off some of your positive energy - not realising that it will only be fleeting and then they will feel the need for more: hence the "vampire effect". Strangely, they often come across as well-meaning and would do anything for anybody.
Ten years ago I shared an office with a particularly difficult example of the breed (proudly announced she was a certified schizophrenic to boot!). Now I can spot them before they enter the building! My main tactic is to avoid: when I had to spend a couple of weeks near our resident "poor me", I got to the point where I wouldn't even exchange basic pleasantries with her (eg - good w/e?). If forced, I would be quite sarky. A classic example of the not being interested in anyone else's life except to prove theirs is worse, a friend dropped by to fill me in on her husband's condition (he had been particularly ill) but we were interrupted by tales of how her "other half" (with whom she'd finished "forever" a couple of days before in front of me - not for the first time, apparently) was recovering from some very minor surgery! We were having a private conversation, for Pete's sake!
My refusal to get involved sent her bowling down to another colleague's desk where she would park her backside and pin her listener in place. Eventually, this colleague stopped giving sympathy and advice which was never acted on and just half-listened, saying what she knew was required of her. I gather the contact has tailed off to a large extent. Maybe you could take that line?
Your energy is too valuable to waste on emotional vampires. You need it and they need to learn to create their own. One good thing I've noticed, they tend to get a new "best friend" every six months or so, once they're drained the last one.