My wife and I always talked about exes, especially the ones who we enjoyed. When I first suggested that she get back with two of her favorites, I too wondered why I said this. I had no misgivings, but why?
My conclusion was simple, it makes me happy when she is happy. (Oh, and believe me, it made her very happy. And she made me very glad I let her, even before we decided that I should be fucking other women.)