its written in our DNA to spread our "seed", so says the scientific proof. an animal instinct if you would; but, i just say its free will, you still have the choice to or not to. everyone (guys for sure) have the thought cross their mind once or twice+ about cheating on their gf/bf/spouse, but its whether you act on it or not. i say, if you can live with the guilt (or if you even have remorse for that matter), go ahead an cheat...you dont deserve the chick you're wit lol.
but to all the dumb females that look away from the fact, you deserve to stay stuck with a dude like that.