Summary: To keep things interesting, and to keep their life's from becoming a monotonous bore, the Cullens exchanged mates every once in a while. But life becomes interesting once Bella is changed and is asked to participate. Multiple pairings. Do not waste your time sending flames. I could care less what you think.
Eternity. That's an awful long time. Eventually, things would get a little repetitive. For example, how would you keep your sex life interesting if you were only with the same person for all of eternity? Alice foresaw that long ago. Every so often, when they moved, they would rearrange the couples. Sometimes Alice was with Edward, Rosalie with Jasper, and Emmett was the lone man out. Or Rosalie was with Edward, Alice with Emmett, and Jasper was the lone way out. But, how would Bella handle this once she found out? Would she even consider this acceptable, and go along with it?