Yea...you may have learned a lesson. However, the fact is that - rather than spending (or a more appropriate word might be wasting) your time mulling over things that might have been, or you hope will be...either do something positive to change your situation, or - stop thinking about it and move on. I know what you're saying, "Easier said than done." Okay, perhaps at the beginning of the process that may be true, but once you get into living in the "now" you start to get it. Is anyone perfect about "letting go." No. Are some people very, very good at it? Yes.
The only person worry, regret, jealousy, guilt and other like emotions affect are YOU. You get the ulcers. You get the hemorrhoids. You get the digestive, stomach and heart problems. Not...the person you're jealous of. They go happily on their way! Nor do the things you're worrying about, feel guilty about, or regret. They're all somewhere out in memory land, ether world, or residing in a fantasy.
So, start the process of re-thinking your life and emotions now. Become a "now-er," which will soon morph into a "now-er/know-er." It will help you in so many ways that translate into a better style of life and a healthier one too. Oh, and before I forget...you'll laugh more to boot!