One ex that was a wonderful person and met and married a guy who apparently was great for her. I often wondered how she is now. (40 plus years later) And another who was in a hurry to get married, found a guy to marry and did so. A few years later I ran into him and they were divorced. She had had an affair with a neighbor and run off with him, though I think that ended also. All of that was 40 plus years ago. I often wondered where her life went. (She was actually a sweet wonderful girl when I first met her.) So yeah. I think of them occasionally.
I think about my past in general a lot to become a better person in the future but I never dwell on my past and exes. There's no sense dwelling on the past because people don't work out for a reason. It's okay to have fond memories and to refine our preferences for future partners though. We can all do a little better each time if we learn from mistakes and all that.
Only enough to be glad I had the experience of being with him, though a pretty shitty one, because I learned a lot from it. I never think about him in a nostalgic manner though. I don't miss a thing about him.