No. Never had the urge to have sex with anybody else while in a relationship.
The knuckle-dragging mouth-breathers who try and justify their wants by saying monogamy "isn't natural" are a joke. You see an attractive person, so that's your big evidence? Gimme a break. Monogamy is the norm in every single country on Earth. Going with their logic, we should be able to kill, steal, and rape whenever we want. That's the way the species existed, right? Yeah... Except most of us figured out that these "natural" behaviors are easily controlled & do more harm than good to individuals and society.
Any excuse to try and get their miserable little peckers wet. Lol.
But, to add to my original answer to the question...
My sex life would make porn stars blush.
So,I have nothing to complain about, either.