Something like Destiny.

If you were born in a place where destiny, and soul mates existed, what would you do? If you were given a necklace at birth and the person you were destined to be with had the matching piece, and every time you got closer to each other, it changed color. Exciting right? But... Then you wouldn't be able to experiment with other people... Because you know it wouldn't last... Take a look into the life of a teenage girl, and a teenage boy, living this life...