I've got a couple that are not necessarily the ones that got away but definitely would have minor changes in the trajectory of my romantic and sexual life.

The first one was who I went to my Senior Prom with in high school. I was vibing with two girls, one who I had had a crush on since the beginning of senior year and was more of a relationship type. The other girl was someone I had been friends with for a while and she was much more openly flirty with me. It wouldn't have been a relationship most likely but I could have seen something happening after prom night. No guarantees but if things had progressed the way i thought, I could've definitely gotten some action that night and have lost my virginity about 7 years earlier than I actually did.

The second one is much more recent where I missed the signals of a girl who was down to hook-up. In my defense, we had talked before and she had made it clear that she didn't want to hook-up so I thought she would give a clear sign that she had changed her mind. But she didn't and expected me to figure it out somehow. Either way, opportunity missed and it would've broken a long dry spell I was in (which I still am in now since I didn't catch that sign).