My thoughts are this could be a midlife type thing and also if you have had some down time plus also maybe at a crossroads in your life?

I think it is really common - 'the one that got away', it leaves us wondering what might have been if we had done things differently. I looked up a lovely guy from my teens some years ago, not to contact, just to see how he was, I had fond memories. He had married and had kids just a bit younger than mine, it looked like he had a fulfilled and happy life. Just knowing this made me feel happy for him. I had always felt regret I had treated him less well than I would have once I had reached emotional maturity.

Maybe having compassion for your younger self is appropriate here? It sounds like you maybe have some regrets. But we live and learn and grow, it sounds like you have.