actually, NTR is a bit worse than just cheating. it's short for "netorare" which means "to be stolen", and as a genre/fetish focuses almost exclusively on a person's despair and feelings of betrayal as they are forced to watch their spouse/lover/childhood sweetheart stolen away by someone who is depicted in the story as being sexually superior.

There's often a lot of exclamations of, "I'm sorry, they're just so much better at sex than you, I can't live without them anymore!" or other words to that effect from the person being "stolen" when the thief decides they want to show the cuckold what they've done in order to break them.



It's not a very nice fetish, not least because in addition to all that's of the above, it's often non-consensual for both people in the relationship that's being broken.