I can sympathize there. I still like meeting new people, but I have a partner now, which makes it harder. Also, I suppose the conversation has to shift a bit; you can only talk about which countries you've gone to before it seems like you're just having the same chat over and over again.

Also, when you're older and have already spent a decade or more accumulating good friends (one hopes!) the exploration/exploitation equation starts to favour spending more time with old friends than making new ones.