Look, I can make a bunch of similar sad puppy stories for the other side of coin as well. People holding it "for the kids" but who wouldn't really stay in case of infidelity. Unhappy people with orthodox religious beliefs who would alas divorce in case of adultery. People desperately trying to fix the relationship and improve themselves not realizing their partner is invested elsewhere and all their effort is wasted.

I sympathize with couples who have a consensual kink however and are now caught in the middle of it. Though I doubt it's anywhere near a major portion of the userbase, they are very unfortunate collateral here. Kind of U.S. govt informers who were revealed by Assange's cablegate (which majority here is positive about), but sans grave threat to their life.

I don't have sympathy for people who make their SOs an unconsenting part of three-way sexual relationship, and yes they are never an excuse short. All people are positive about their self image, and rationalizations of abhorrent actions are a natural consequence.