"how do you feel when you get these reunion notices"
They are fantasy on a person’s part. And they usually lead to mid life crisis on another’s part, so affairs, broken marriage etc. And usually towards people you no longer know as people!
ITS NOT REAL, its memories of something that is now well and truly gone, the past. Oh I "loved them when I was 16", but now I am 40 and in truth I have never seen them since I was 16,,,hello
Go back to the real life you have experienced for many years since then,,,as that’s real.
But if some are so insecure and unhappy, go and meet new folks, as very few can turn back the clock, as its just in some folks heads, a dream. And only that, sorry for being do harsh, but its the truth. Whats in your or others dreams or memories very rarely makes a good or new reality