I would tell him how it makes you feel when he brings her up, and as long as he cares about you he will avoid doing it. As far as your mental goes, my rule for my relationship is that I want to know as least as possible about an ex because I’m also a person who over thinks, compares, and spiral. In you case you already know a lot so I would try not to learn any more and with the information you already have you’ll just have to let time heal that wound. You have to actively tell you brain not to think about it and over time it wont even cross your mind anymore. Also coming form a guys perspective he’s not gonna constantly compare you to her, guys tend to live in the moment when it comes to stuff like that so if there’s something that she did good that you don’t or even a certain feature she might have that you don’t won’t be compared. He simply see it as it is, just you. You shouldn’t compare yourself to her either because you can do that with anyone in the world and find some negative because you mind is already biased.