So let's say you're a romantic. And let's say a relationship has recently ended, painfully so for both. And let's say you know you should be sleeping but can't stop tossing and turning because you're fixated on the nature of love. Who winds up with who, and why? Why do we choose the people we do? How does it happen? Why the yesses, why the nos? I would hate to think it's just chance, although I suspect that's at least part of the answer.

If anyone is bold enough to answer this question, what makes you fall in love and what makes you fall out of love?