Agree 100% with willsrvu ... penis size doesn't necessarily make a cuck. An unhappy wife over your "penis size" probably will, eventually. I have known of several guys who were adequately "hung" who's wives cheated on them with other men. We guys are so infatuated & focused on our dick sizes as proof of our masculinity.
I will say this about dick size ... it seems now that more and more women are starting to become curious of larger dick sizes BECAUSE they are being convinced that the larger dicks will give them more pleasure ... again, not necessarily so. As use to be said "its not the size of the pen, but how one signs his name that really counts".