Polly is more like cheating than NTR and didn't expect that 😅
Yes and no. I wouldn't call the cheating story NTR if the SO never even appears in it and isn't made aware of the affair. To me at least that's a separate thing. There needs to be some level of awareness and discomfort for it to be NTR. Otherwise it's just cheating or NTS.
But in this case I agree that it's mostly NTR.
NTR is not literally what the word means, its an entire genre, and the genre is a lot more flavorful than "just cheating". It can involve significant people that arent SO, like sisters or mums, its more about the taste of someone taking away from you someone important for you, thats why "just cheating" its quite lame in comparison.
Also OP is right, Polly is just cheating and its kind of the most boring of all the girls.