Once I spent six hours of a twelve hour Greyhound ride sitting across the aisle from a couple who had met when they sat next to each other, and apparently, discovered that they were two halves of a sundered whole. Or something. When we hit El Paso, they were going to part ways, she for Tucson, he for Denver. Off to lead their lives, I suppose, I never caught the exact story.
They spent their time alternating between discussing the deep and abiding parallels between the courses of their respective lives and worldviews and making out under a blanket. At the time, the whole thing made a deep impression on me.
Assuming that what they thought they had was honest, which I suppose nobody can know but them, think of the existential conflict involved. Assume that you have one perfect soulmate: would it be better to live your life in ignorance of this fact, making do on your own, or meet that person exactly once ever, for a few hours around midnight on a cramped bus full of poor students and day laborers? It's been a year or so since then, and I wonder if they still think about it. Probably they've just laughed it off. It's the sort of thing you would really have to diminish in your head, to be able to keep on going.
I've got an image in my head, a scenario. One of them, thirty years from now, old and broken by the world. Drifting through the crowds in some great city, and seeing the face of the other in the crowds, and then blinking. Gone.