It's always so odd to me to see people lamenting that they're lonely and don't have a lot of friends, that they don't know how to make friends as an adult, etc, only for them to reveal that they.... have a whole-ass romantic partner or person they are married to!
My incredulity is not directed at the idea that someone who's romantically partnered might be lonely and unfulfilled in their social life, for the record - that part is intuitive to me. (My best friend is the closest thing I have to a partner in my life, and we have both periodically expressed at various points in time that we'd like to have more friends.)
It's more that... well, how did you meet your partner? How did you grow closer to them? How did you navigate forging the kind of relationship you wanted with them? How do you maintain that relationship now? Are there truly no social skills involved in that process that you can transpose onto the process of making friends?
It's hard for me to wrap my head around because to me, navigating dating relationships or sexual relationships seems so much harder and more fraught! It requires much more subliminal communication, much more weighing of "is this contextually appropriate to bring up?," much more active scripting. Becoming friends with someone just requires indicating to someone that you like talking to them and want to spend more time with them. That's relatively easy.
I don't know if it's that a lot of these people are straight, and so there are much clearer social scripts and rituals involved in dating relationships (although I sometimes see similar sentiments from queer people on here). I don't know if it's that a lot of them are women, so they've been able to be somewhat passive in the formation of their romantic relationships and aren't used to taking the initiative in relationships in general (though "men hit on you all the time and you don't even have to work for it" is... really not my experience of being read as a woman).
It's just bizarre and kind of alienating that so many people's perception of these social rituals is the exact inverse of mine.