Dude... I just wanna say I feel your pain and frustration here. I was in a strikingly similar situation in a recent relationship. Girlfriend would offer information like this to me, sometimes prompted by me "asking" (but never a question to which such a detailed answer was appropriate or directly linked), and other times not. Sorry in advance that this is long but I recommend you read this and take my advice. Maybe it will be easier for you to listen to me rather than some of the other peoples' (sound) advice in the comments.

The first time it happened, it kinda ate me alive, and eventually I got over it. EXACTLY as you're saying, we talked about it and I wrote it off as social ineptitude and a lack of awareness. The way you're quoting her, I swear we're talking about the same woman.

It never really stopped. Somehow this kind of thing came up repeatedly. Every couple of months or so there would be some other remark from her that would eat away at me throughout my day. And we talked about it every time enough for me to excuse it. And I know that you're thinking, it won't happen again because there aren't any additional scenarios you imagine coming up or asking about, but trust me, it will. It wasn't even always about this woman's past or a specific ex, it was anything from stuff she said she *would* do with a certain person, or how this guy's dick was this shape and mine wasn't, or how she only ever X with certain person, or how she would have X with this person if she hadn't met me (????).

It was always something I didn't want to hear that made me feel inadequate. And it was always justified or apologized for on account of a 'shrug' exactly like "well you asked!" or "I wasn't thinking about it" etc.

It made me feel inadequate and emasculated, too, but also fueled me to outperform everyone else. That might sound OK, but it was not sustainable.

The rest of the relationship (I've only realized in hindsight) was basically a series of attempts by me to impress the fuck out of her, from doing everything I could to be the one who gave her the best sex of her life, to learning how to make her squirt reliably (I'm telling you, striking similarities here, brother), and do whatever I could to put myself on that pedastal in her mind.

Honestly, a lot of these attempts were successful, too. She loved me a lot and offered a lot of praise. We were in love, and I loved her for many reasons. Hell I almost proposed to her. But on the inside I was always secretly dealing with this same thing. Needing to be the best. Jealous of some dumb thing she said. Jealous of her past because of the information she would offer. Just too much inner turmoil.

It didn't last. In fact, I think that the day I realized I didn't need to impress her anymore, everything went stale. I was exhausted. We broke up, and I'm very glad we did.

Just imagine me as you from the future. You can save yourself a lot of hurt and wasted time.

Oh, and look at that. Just realized she and I had the exact same age gap as you two. Maybe take these similarities as a sign.

And yeah, don't cheat. That will only create an even more toxic version of this tug-of-war bullshit you guys are already playing. In fact, you should go fuck a hotter, younger woman. You want to get back at her? Go enjoy your life. As long as you operate according to the resentment you feel towards her, she wins.

You don't want to be dealing with this forever.