Before we continue---everyone who says no is lying. Men (and most woman) are only as faithful as their options (as the great Chris Rock once said).....No cheating = No options....
Morals and integrity = people that need rules in order to live.
If you are with your old lady (or man) for more than 2 months and the hottest chick in the world came up to you and offered one night and a million dollars, I am sure you morals and integrity would go straight out the window.