The reason of love formed thousand years ago. The seed come to the tree. The friend come to the lover. It seems everything has its destiny.I don't know why we meet each other and fall into love but I'm extremely sure the reason of love formed thousand years ago.
One word in Chinese is "Lun Hui". Lun means the round. Hui means coming back. In ancient time in China people believed the after-life will be reborn and the life will start once again in another shape which depend on what you have done in your this-life. If you are good one you become person again or you will be a dumb things like pig and dog. This is Lun Hui. So we usually say, once life is once Lun Hui from birth to death.It just looks like a round.

So concerning the love,people believe it's also affected by Lun Hui.In this-life two people become husband and wife just because of something in their before-life.Maybe they rided the same boat. Or a fishman freed a fish princess for his mercy and the princess pay back in this life.
Lovers hope they can always be couple in their several Lun Hui.