Most of my friends who I've stayed in touch with were from earlier in my life, when making friends was easy-peazy. But people move, and I've become more selective, so I don't don't attach to people willy nilly anymore. My best friends are the ones who have worked as hard to stick with me as I with them. Put another way, those who haven't let time and distance degrade the bond.
My best friend lives 6,000 miles away, and my favorite local friend just split with his wife and moved to another city. Except for a couple of neighbors and and my ex in-laws - none of whom I socialize with much - my main social circle is workmates. They're a fun bunch, so that's a good thing, but for the first time in my life, I don't have a hang-around buddy. I need to join a knitting club or something.