I always felt like that but even without a gf, anon.
it's like there's a secret exciting world outside your own, where people around you go to, and you find out later... when you feel excluded and left behind.
get used to it, stop thinking about it and enjoy what you have now. you never had that, you never will, thinking about it makes it worse because you can't do anything about it.
this comes from a 28 virgin dude who found out when I was 13 that there was a meeting place for my peers to make out randomly with each other, and most of them were also fucking. of course, when I showed up they all went away.