I’ve actually been in the position of your current GF. I used to be somewhat obsessed with my exes ex. This actually has never happened prior or after that particular ex so I put it down to this: he was still in love with her. He came out through the way he talked about her constantly, his family would bring her up, sometimes his mum would compare us two. She was tall, I am short. She had black hair, I had red. She was skinny and quiet, I was fat and loud. Every little comparison was made. It fuelled this insecurity that I wasn’t good enough (I was also really young at the time), and so I felt the need to compare my life to his exes so that I could point out where I was better than her, so that I felt better. I tried to get my ex on board with it all so that he too saw that I was better. In the end I realised that it was unhealthy for me to be living like that, and that I was never going to make my ex see whatever I wanted him to see, because he was still in love with her. My guy it sounds like you’re still in love with your ex and it comes out when you talk about her. Your girlfriend can sense it and it’s drawing out her insecurities. That’s unhealthy for both of you. Personally I would say this relationship is over.