Look man, nobody who is dating anyone else should ever have to deal with that. I myself have had to deal with talks about ex's and even though it was never quite like your situation it made me feel small and as though I wasnt good enough. If she really cared about you in the way that she should, she wouldnt even want to talk to this guy, because she wouldnt think about anybody but you. It all sounds kinda harsh but its the truth....Good luck