The other day I went to a local small community theatre to get myself out of the house. Despite the crowds and noise I felt relatively fine until the play started and I recognised several of the class were people I knew at an old drama club I used to go to. The fact that they were on stage performing is exactly where I want to be in life. Needless to say this made me very envious and self conscious about my social-less lifestyle. I ended up running out after that embarrassed and feeling very bad about myself.
Sometimes I feel that way when I look at people I used to know when I was 14. They've all blossomed out of their awkward phase and into social butterflies. I'm still me.
It would have been fine to stay. You have as much right to be there as they do.
I get this problem too, however after secondary school and into college, I just lost contact with them, nowadays I kinda force myself to stop thinking about it because it grinds away at me so much, that they are so successful and im not etc :/