It would seem, from a logical standpoint, that being cheated on would make you less likely to cheat simply because you would know what it felt like. How much it hurts. But everyone is different and love or lust does not always follow the rules of logic. So, whether being cheated on would make a person more likely to cheat or be faithful depends entirely on the individual involved.
Well, take it this way. They know what it feels like, I don’t think that they will actually want it to happen to someone else, especially someone they love.
I think neither. I think their core values will remain the same and they will do what they always would have done. If they are someone who would not have previously cheated, their feelings towards not cheating would probably intensify. If they are someone who may be inclined to cheat, they may use that experience to justify future infidelity.