My friend keeps on getting attracted to married/committed guys too. I think it might be because that they are married, it subconsciously shows that they are wiling to commit to one person (which is pretty hard to find these days).
Plus I think it could also be a result of the idea of forebidden fruit, wanting something you're not suppose to have. I think this is true of my friend because when the married guy wants to take it further and have an affair with her (the little charmers!) she doesn't.
I don't understand her and she hasn't come up with the forebidden fruit idea or any of the above, this is just my conclusions from being an unbiased observer.