Adulthood is missing more people than you currently see. And nobody warns you about it, either.
I've got people scattered over half the world, who at different times were my everyday folks. And now, not. Adulthood is achieved at the point where those people you'd like to see outnumber those people you do see.
Or else, it seems like it must be. And some of my prototypical grownups would seem to have the same experience.