I'm reading Plato's Symposium kids. It's all about love but will talk about that later.
This was a funny description by Aristophanes who is at a dinner party with Socrates and he describes how primeval man was round with four hands and feet, two faces, and could roll forward on four legs like a barrel. That would be so funny to see eh?
Alas, they got uppity and challenged the gods. So Zeus cut them down in the middle and Apollo fixed us up by fixing the cut, fixed the belly. And then because the two separate halves couldn't live together, they started dying off. So Zeus made man and woman separate.
But deep inside you, lives the seeds of that primeval man. So when you meet your soul mate, you cannot explain what you want from her/him but just want to be one.
It's obviously not medically right or evolutionarily correct but a nice explanation by the ancient Greeks eg?