Longing

Something very strange happened to me on the train today. I get on and have to stand for the first two stops, but then a seat clears. I walk over to it and start to sit down and, as I do, the train doors open for another stop and the couple sitting across from me gets up and leaves. And in a matter of seconds, I felt the pang of loss. I missed those two. I didn't know them and couldn't even point them out on a street, but I genuinely was hurt that they left before I could meet them.
Why? What does it all mean? Will these pangs happen often when strangers exit? If so, I'm in an assload of trouble. I see strangers often. I mean daily. I can't go through life missing people I never met. That's crazy. I'm crazy. The only sane thing about these moments is the exiting of strangers. Strangers should exit. It makes sense. The train stops near your home and you have to get off. Maybe if I keep telling myself that, I won't cry every time I ride the train.