If you don’t make a conscious effort and invest time into creating new friendships (with considerable difficulty since you yourself are tied to “adult” obligations), you can end up alone with withered social skills before you realize it.

One of the things I did when I was in my 20’s and 30’s that I’m really glad I did, was to always be willing to relocate. I did it about 5 times for new jobs, once for a new school, and twice for a romantic relationship (including with the woman I ended up marrying). I made new friends in each city, and kept those “new friendship” social skills over time. Now I’ve settled into a specific place with my family, but I have friends all over the U.S., know a little bit about a lot of cities and their neighborhoods and the local culture, and perhaps most importantly, know what I’m looking for in friendships and relationships.

I made new friends in my 30’s because I absolutely had to, living in a city where I only knew one other person. And now I’m still making new friends occasionally in my 40’s because I like to: colleagues and neighbors and fellow parents from my kids’ schools, etc.