Depending on how late it is, I can get seriously upset. Like, I've cried myself to sleep because I saw 2 people playing Overwatch together. I've thrown a tantrum over in Brainbent over something similar, can't remember what it was. And just now I had to stop myself from tearing up after I saw someone casually mention "playing DnD with their friends" Jesus Christ what's WRONG with me?!
-sympathy fistbump- I've had some similar issues in the past. If it helps, wanting to be included in the fun is absolutely a natural response. The extent to which it is affecting you isn't, but my best guess is that your reaction is being exacerbated by brainweird or abuse, because those are the things that tend to pump up those kinds of feelings.
witnessed, dude. I have much the same problem! particularly memorable was the time I spent two hours crying after seeing my best friend at Starbucks with someone who wasn't me. unfortunately I don't think I can help much with figuring out what's wrong and what you can do it fix it, partially because I myself have not had much luck combatting my irrational jealousy and partially because, while I'm fairly sure my sensitivity in this regard is caused by brainweird, I have no idea which brainweird, so I don't really know how to address it. but yeah. you're not alone.