My girlfriend avoids taking about a guy she was seeing during our breakup—should I be concerned?

Me (23M) and my girlfriend (24F) have been together for almost 9 years. We broke up in April or May 2021 (I don’t remember exactly), and we got back together in early 2022.

During our breakup, she was talking to another guy. I never made a big deal out of it, but whenever I bring him up, she gets defensive and says, “Why do you have to bring that up? I’ve been trying to remove him from my memory.”

Her reaction makes me wonder—did something happen between them that she deeply regrets? She once told me that he took her to his place but reassured me that nothing happened. However, the way she avoids the topic completely makes me question whether they were physically intimate in any way, whether that means having sex or other intimate acts.

I try not to dwell on it, but whenever we’re intimate, a part of me can’t help but get glimpses of what might have happened during that time. It’s not something I want to feel, but the way she avoids the subject makes it harder to let go of these thoughts.

I don’t want to accuse her of anything, but I do want to understand the full story. How can I bring this up in a way that encourages honesty without making her shut down the conversation?

Any advice would be appreciated.