Re: why does my guy....
Well...I wouldn't put up with someone who frequently talked about his ex in front of me, no matter the context. Have you ever told him, "Look, I don't like hearing about your ex all the time, could you have a little respect for my feelings please?" If he doesn't stop or doesn't really care, well then it's up to you to decide if you want to put up with it or not.
The grass is always greener on the other side...until you get closer and see that it's astroturf~