Yep. First noticed this with friends who got married in their early 20's. Suddenly those friends weren't around and available to hang out as much as they had been. I really didn't think I was heading down that road anytime soon until this year when I got into a serious relationship and slowly but surely enough your old buddies get replaced by "couple friends." Not a bad thing really as I probably need to grow up and mature before I become the "old guy" in the bar/club and some of my friends were kind of a drain in their own ways, but couple friends are way more boring than your single and unattached friends. It's weird too because couple friends have way more money to do fun things than your borderline-broke single friends so you would think they'd be more fun but I guess getting older and having bigger responsibilities has a sobering effect on most people.
I hate couple friends, I don't like that whole dynamic. Honestly, that just isn't me and my girl knows that.
It's like I have to pretend to be having fun because hey it's our couple friends, it's like a snooty ass way to look down on single people. Like you can't associate with someone whose fukking random people, like they`ll corrupt you or something.
Plus like you said, couple friends are boring. It turns out to be an ass-kissing fest.