There's important nuance to it.
Do I want to watch my wife or gf who I thought was totally loyal and loving cheat on me with someone? Especially if its done in a manner especially to be hurtful? Absolutely not.
But for me, that's completely different in a couple deciding, either beforehand or on the spot, if they want to swing or engage in some sort of group sex or relationship where they both can hook up with other people, and I think that those situations are really hot.
As to the other, fucking a woman behind her husband's back is never something I'd do IRL, but in the sense of a sex video game, it can be a hot power fantasy. Especially if the goal is to be a hot stud who seduces women and takes them away for yourself.