GF cried during sex with her ex, never with me.

Me(m23) and my gf(f22) are together since 2 years now and we are happy and doing well together. Even moving together is slowly getting a thing. We see us min. once every two weeks, sometimes more. We doing stuff together, we are doing things on our own, give each other enough space. Sex is great, not as frequent as it used to be but still as great as in the beginning.

Early into our relationship at one point we talked about sex and she mentioned her ex (which was her first boyfriend and sexual partner) making her cry during sex because it felt so good. I found that odd but didn’t thought about it much. Now tho it starts to sting. I never managed to make her cry of arousal. Somehow it makes me feel less. I know thats stupid but this feeling keeps comming back.

How do i stop comparing me with her ex and just get that out of my head?

Its my first relationship and i guess my problem are some insecurities and the feeling not being good enough.

Thanks for any comment.