I don't know why everyone assumes the break up was Justin's decision and had nothing to do with Jessica. From what I can tell, neither of them would stay someone unless they wanted to be with that person. I think the split was mutual like they said. Jessica may not be the most famous side of the couple, but that has nothing to do with how their relationship ended.
Four years is a long time...I doubt either of them would stay with someone they didn't care about for that length of time.
But It would be great if Jessica dated someone like Ryan Reynolds. I can see that working...after he breaks up with his supermodel, of course.