Not to counter completely your point, but I have no desire to have sex with a woman who is doing it as a sacrifice...if she doesn’t want to be having sex with me (unless there is a legitimate physical or emotional reason) any longer, I will find it elsewhere, as will nearly every other person on the planet.
I don’t condone cheating, but it is absolutely unrealistic for any woman to deny her husband sex routinely and then be upset when he goes elsewhere for it. Same would be true if the roles were reversed.
But getting back to my point, if a woman doesn’t want to have sex with me, but is just doing it out of sacrifice and duty, then it sure wouldn’t keep me from straying... if you treat sex like a chore your partner will stray, its only a matter of time.
As to the specifics of this case, who knows why this guy was fooling around, but the fact he was doing it so flagrantly just shows stupidity.
Sounds to me like you’re single and still fairly young, maybe under 35.
If you do marry someday, and hit 50, and still love your wife, you’ll have a different opinion.
You’ll also learn that sex with the one you love changes as well.
All the best -