Hmm interesting question.
I think they date people who they suspect won't leave them or who will put up with their crazy behavior. But I think the reasons could be different. From my last BPD waif bf (who dates a LOT of girls), I notice these to be some of the "types" he goes for or stays with:
1. Less attractive/less confident/insecure girls
2. Girls who like to fix people and/or save the world. I guess nurturing/motherly types fall into this category, too.
3. Girls who are clingy and/or loyal to a fault
I think I fall into the second and third categories. He played on this aspect of my personality in the beginning and it made me fall for him pretty hard. He would come to me for soothing when he was stressed or sick (just verbally, though, as it was a LDR). He would even explicitly ask me if I was going to protect him. I think he sensed that about my personality by that point and he knew I would eat it up
. I'm the loyal type, too, who fights for love, which I showed him when I stupidly flew out to see him after an argument that was really his fault (dumb move on my part, but it was an amazing trip nonetheless). As for the third category, I have seen how he plays on girls' insecurites. He tests to see how insecure they are at first. He will do this one thing where he will joke about adding your cute girlfriends on FB or ask if you have any hot friends. Based on a girl's reaction, he'll know how insecure she is. If they are, he will know he can get away with more crap and the push/pull stuff.
They really do have some sort of radar for these traits. It's so uncanny. I wonder if it's innate and instinctual or if they do it consciously. I know they do the "testing" but I wonder if that's done automatically or if they know they are doing it. Either way, it's fascinating, and also insane!
Btw, I think I would consider #2 as being a "complementary personality trait" to a BPD, whereas I'd consider #1 and #3 to be traits that they can use to manipulate/take advantage, but not necessarily "complementary personality traits".
