Sure, but those that can't have the option of just not going into a relationship or breaking up.

With cheating, you don't have that option. By the time the person cheated on learns about the cheating, they might have been years with the cheater and passed over other potential relationships that might have been made them happy. They might have made sacrifices for the cheater. And at no point, they were given the option of leaving if the idea of their partner being with another person is something they can't accept. They are forced to deal with that situation regardless of how that made them feel.