I am so lonely and I feel like I can never escape it

I'm 24M, never had a girlfriend, not in school, and I don't really participate in many activities so I don't meet new people very often. I have a few friends with whom I do stuff with once in a while, but they don't really hang out much with each other, so when I am with one of them and the others aren't there, it feels like I am alone again; as though I am not with my friend as part of a group, but rather as this perpetual sidekick. It's a very lonely place to be in. I don't know where to go or what to do in order to improve my situation.