Why does he mention his ex-girlfriend?

I've been talking to this guy lately and I really like him. No we're not dating yet but we flirt and he calls me pretty and we talk all the time. He asks me how my day was and always calls/texts me in the morning to know if i slept well and to say good morning and other sweet things like that, but he got out of a relationship like 2-3 months ago. They were together for a little over 2 years. She broke up with him, and he's mentioned her a couple times in the past week. Guys don't like when we bring up our ex boyfriends so what makes you think we like it when you talk about your ex girlfriends? Why does he still bring her up? Does he still have feelings for her? And if so I should probably back off a little because... I don't really want to be a rebound to be honest =/ Ive been there before it's not fun. Also, I see her a lot but she doesn't know he and I talk, i don't even think she knows that I know him... which also makes me a good target for the rebound since there's a small chance she might see us together and want him back. Maybe I'm just too untrustworthy toward guys but forget that, just answer my first question, why does he still mention her?Why does he mention his ex-girlfriend?
Well i personally think two years is a long time. They probably did a lot together in that amount of time so it could be he just has storys and she is in them. If you are close to him and you know he is a nice guy then i wouldnt worry about any of that other stuff. hope i helped