Let's translate that philosophy to other "wrong" activities, shall we?
"Spending money is more exciting when it's stolen. Saving is much more meaningful if there is the possibility that someone can steal it."
"Life is more meaningful when someone is actively trying to kill you. Murder is much less exciting because it's wrong."
You see the problem? The notion that actively doing something awful to someone else makes what they have meaningful, and what you are doing exciting is just selfishness and justification.
You don't like monogamy? No one is forcing you into it. Unhappy with your [life | partner | marriage | whatever] and you think the answer is outside your agreed upon monogamous relationship? End it. Divorce is legal. Breaking up without marriage is even easier. There is no tyranny is a relationship you enter into of your own volition.
You have children? Don't be an asshole and hurt their other parent because you have issues. End the relationship before starting another one. Be the person your children can respect.
The other person in the relationship? Don't be that. Because you are being a party to deceit. No, you aren't the one cheating, and that justification only goes so far, but it still shows a base selfishness that informs your character. You ought to expect to be hated, because that weakness and selfishness that makes up your character is the instrument that harms someone else. In the pain that is being caused, you are the weapon that is being used by the person cheating to hurt their partner.