To me, a relationship doesn’t need two people to maintain and keep it going: it only really needs one, so be that one person!
I realize people are busy and have their own lives, but I still call, I still ask how they are, I still ask what they’ve been up to. Gestures like these are tiny, tiny investments that pay off in the form of a rich, robust social life.
Nobody has ever told me stop reaching out, stop trying, but if they did, of course I would.