So I just started reading through this again, after stopping around chapter 33 or so, and having a character try to NTR a person and then suddenly change into BSS, is, wow, did not expect that, legitimately. So shocking I decided to make a comment.
I always get confused at the terminology of NTR. Doesn't it require a pre-established relationship being destroyed by a third person?
When it's just a dude/girl watching on the sidelines feeling jealous of two friends showing off PDA's, doesn't everyone deal with that everyday? I know I do. Maybe I'm exposing myself now
Yeah that's NTR. It is also used for the 2nd thing you described, but even JP people think it doesn't fit that, so they coined a new word called BSS (Boku ga Saki ni Suki datta no ni = Even though I loved her first) which is when your crush gets stolen by someone. Its apparently classified as a subgenre of NTR.