CartesianFart
Deity
Nah.Just doin some unconventional thinking on the semantic of 'cheating'.you have a strange grasp of what's right or wrong for sure....
This is a good question and I would say that as long as you are not discovered by anyone to pin you to the crime then i have to concede that it is not the case that you are a "killer" as defined by the community of individuals but as a "killer" being defined by your own secret of knowing you have committed such act.so if I kill somebody but am not caught, I didn't do it?
But,some couples consist of one not adhering to the principle of monogamy and the other changed over time after the mutual agreement occurred.Both situations you stated sure are cheating by any sensible definition. The only way when sleeping with somebody else is not cheating is when you agree to allow this in your relationship beforehand...(basically what Eran said).