" Oddly enough, after viewing some of the discussion on the comment thread, I realized that my judgment might have been a little harsh.
I'm not trying to generalize, but most of my female friends talk about past boyfriends, dissecting why their relationships didn't work.
On some level you must have known that she would be bothered by it, and you chose not to tell her.
From "he just doesn't get me" to "we're too different" to "why did we stay together THAT long," women tend to overanalyze past relationships.
However, the one thing that seems to be the unwritten rule among us is that we would never even consider dating our friends' exes. But now I realize this rule really needs more thought, because I believe there are two factors to consider before answering my girlfriend's Facebook question.
If she truly wants her ex out of her life, she can’t very well do that if he is dating her close friend.
It seems like you chose a relationship with him over her, and there isn’t any going back.