Why do we always go for the jerks and shun the ones who actually love us?

I was talking to the girls at my work, and they both have ex-boyfriends who loved them and treated them like gold, but they dumped these guys to date jerks who take them for granted. Then when they're hurt, they call up their nice ex-boyfriends to make them feel better, even though they feel guilty for using them.

I realized that even though I'm in a long-term relationship, I also sometimes like guys who treat me like crap and when I feel bad I look to my boyfriend to make me feel better.

Is this a girl thing, or do guys do it too? Any insight on why so many of us do this?