I’m in the same boat with my significant other and myself being each other’s only close friend. I don’t know if it’s healthy, but it seems to be pretty common. I’ve noticed most people in their 30s or 40s don’t really have close relationships outside of their partner, kids, or immediate family.
I think a big part of the problem is that there are genuinely few available means of meeting new people. Everybody suggests going and doing group activities to meet people, but how many people actually make real connections this way? I’ve spent years on various groups with nothing to show for it outside of superficial acquaintances that hold me at arms length, always having an excuse when I suggest hanging out one on one.
Not to mention, group activities exclude a lot of people, including ones with social anxiety, autism, physical handicaps, and the immunocompromised who can’t risk getting sick from spending time in a crowded space. It sucks that there are literally zero options to meet new people one at a time.