It used to be, when I was a lot younger, that I would be pretty indiscriminate: as long as someone wanted to spend time with me, and they were nice enough, and we could find something to do together that we enjoyed, like watching a movie, playing a game, or just hang out and talk about something (usually meaningless), that would be enough.
But as I got older, I started to see that as a waste of time, and started to notice how little I had in common with the people I spent time with, and how rarely we talked about or did anything that was really meaningful for me, and it started to bother me.
So, over the years I've lost touch with most of my old friends.. and, as I'm not very social, and I'm usually quite content with my own companionship, I really haven't gone to the great trouble of finding new friends, especially now as my standards have gotten so much higher.
The result? I've pretty much no friends left. Occasionally, someone at work reaches out to me, but, really, I recognize that we have little in common, and I usually don't respond in kind. So I'm pretty much alone, and probably will remain so for the rest of my life. Usually I'm ok with that, but sometimes I notice some couples or groups of friends around me, having fun, laughing together, and it bothers me. But not enough for me to make a big change in my life.