First, I have no idea what guys are talking about when they say their wives get all stretched out permanently by a huge cock. I'm a father four times over and each time, within a couple of days, the mothers were as tight as they were before the children were born. There's no way a cock will permanently destroy her.
Secondly, for those of you that have requested it, I also have the fantasy of sharing my wife with another man and my wife finally acquiesced and made my fantasy a reality. I have posted about it elsewhere on OCC, but I can retell it here if you'd like me to.