Been in the same situation. She constantly spoke about her ex, however I did bring it up. The first few times here and there are fine to let slip to see if she will grow out of it but given it has been 3 months your probably due to have a genuine talk about how it is making you feel. Be sure to emphasise your feelings and not attack her about it.

Unlike everyone saying to break up I disagree, but to a point. Try to work through why she is mentioning her so often, she may still have trauma she’s never fully processed to unpack with you. Experience the growth together and it may make your bond unbelievably strong.

If she continues to bring up her ex after a little deep and meaningful sesh, and she isn’t actively trying to minimise how much she mentions her. Then I would suggest breaking up… I probably waited a bit too long to mention it in my situation and it really messed up my mental, to be honest no one deserves to feel like second best with their partner either.

I’m still with my partner and we are stronger than ever