Due to my career - for lack of a better description of the better part of my time on this rock- my different groups of friends has for the most part been - transient..I guess.
As in this definition of transient :
https://www.thefreedictionary.com/transient -
"1.Personnel, ships, or craft stopping temporarily at a post, station, or port to which they are not assigned or attached, and having destination elsewhere.
3.An individual awaiting orders, transport, etc., at a post or station to which he or she is not attached or assigned."
...if you allow me to Skew those definitions a little bit.
Transient, as in too many years in the Military/Government Contractor life(?)
I have a small group of friends that have continued from my childhood, school and pre-military...life?
Nearly all of the other 'groups' are, as I said...kind of transient.
Most of the different groups are loosely connected by Department or University or Bureaus, but rarely share very many actual individual personnel that remain year after year.
What really amazes me is that the Friends that have gone out of their way to keep in contact or actually visit me in hospital(off and on, in and out)for the last 15 years or so is really quite eclectic(?) as in originating from relationships from all different areas of my carrer/life...
To be honest, Wegs, most of my closest 'friends' now weren't the people that I ever thought would be close to me when first meeting/working or becoming associated with them!
If nothing else, life can be pleasantly surprising and quite enjoyable if we just allow friends to develop...naturally, maybe...
You know, without demanding that anyone must meet certain requirements or fit certain molds before we give them any opportunity to share in this wonderful continual Amusement Park-like- ride we call life.
Sometime, somewhere, someone said "It takes all kinds"...and I gotta pretty well fully concur wit dat!
Meh...I rattle on these days...
Wegs, have you ever heard of any reference to a "Monkeysphere"?
Maybe do a duckduckgo.com search of Dr. Robin Dunbar Monkeysphere Theory.
In my estimation it touches upon what you broached in your OP, Wegs, and I honestly think that you will find it, at the very least, interesting...