YANBU, but like you I sometimes worry about this.
I was every sociable in my 20s and early 30s - couldn't bear to not be out on Fri and Sat nights, always wanted friends round etc.
My DCs are still primary age, so I have plenty of school-gate chat. But they are both old enough to go to friend's houses without me, so I'm not always involved in their get-togethers.
I live in a village which is quite sociable, people go out a lot in the evenings, have dinner parties and so on. And I just can't motivate myself to get involved. I'm a single parent and I work, so I'm constantly shattered. I love the moment when the kids are in bed, I've done all the chores I need to do, and I can flop on the settee in my pyjamas. I'd rather stick needles in my eyes than get my glad rags on and go out to socialise.
By I do worry slightly that I won't always feel like this, and one day I'll have the energy and enthusiasm for a night out, but I'll have no friends left to invite me! That said, I make an effort to keep in touch with my really good longstanding friends, even if it's just phone calls and emails. And sometimes we meet for lunch, which I enjoy because it doesn't interfere with my sleep!