AIO Husband confessed being flirty with college friend

My husband (44m) and I (45f) have been married for 20 years. This past weekend he casually mentioned that he and a female friend (who is now married to his college roommate and who we see all the time) had an “energy” between them in college. He described it as lingering stares, hands resting on knees a longer than is normal for mere friendship, stuff like that. He said it was happening while he and I were together (I graduated a year earlier than him, so we were in a long distance relationship for a while) but it “cooled off” a lot once we were engaged. Apparently at one point before our engagement they were drinking at a party and after they left she invited him into his room, saying “no one would know.” He says he answered that he would know, and she mumbled something about him being a good person and that was that. He says he went on a walk with her a few days before we were married and they talked about how this thing between them had to end. After that they only interacted the way normal friends would. He told me this story like it was amusing, and I acted like I thought it was, too. The truth is, I’m a somewhat jealous person. I don’t love that about myself, and that’s why I laughed this story off with him, but honestly I felt really hurt for the girl I was 20 years ago. She would have felt so devastated and betrayed and…foolish, I guess. I also feel a little weird knowing that this friend, (who we see all the time,) once tried to get my husband to cheat on me. She didn’t know me at the time, but I still sort of feel like “what the hell?!” I’m obviously glad he didn’t give in to temptation, but I’m also a little angry with him for playing these games and making her think she was justified in coming on to him. Had I known it at the time, I might not have stayed with him. I know this is all water under the bridge, and I’m definitely not worried about this being an issue now….if anything, they often don’t get along and their disagreements can get awkward. I don’t even know what I want….maybe an apology? (From him, not her. I don’t plan to ever tell her that I know about it.) Is that a stupid thing to want after all this time? I just feel a little shitty about the whole thing. Am I overreacting?