It's all in the definitions. My husband knows about my extra-marital flings, and approves, and often times is present. This guy's wife is unaware of her husband's actions and probably unapproving. I ended it partly out of respect for her.
There is also the trust between me and my bull. I don't like being lied to. You can be the best lay in the world, but lie to me and your ass is out the door.
Finally, it is a safety thing. I don't know this woman, and I have no intention of being confronted by a psycho-jilted cheated-on wife in a dark alley.