As far as I understand, NTR refers to some specific sexual relationship. However, here, and even more elsewhere, this term is used as if every sex relationship is NTR, which it is not. Judging by the picture, I would conclude that a threesome follows.
Ntr is referred to a little loved one being stolen away from SO emotionally. Its different from cuckolding that has some level of concent between SO and partner.
Here Jill could be drawn away from mc/Tremelo, with a chance of her cheating.
Its a play on negative emotions such as betrayal, theft, jealousy, sadness and humiliation.
As BAD is a guy multiple potential options, any girl who he has a relationship with that sleeps with someone else, could arguable be a situation of ntr. or just cheating.
Time for Tybalts payback, steaming all the girls from Tremelo. Since its basically all those feeling he must have felt, seeing Jill fall for Tremelo.
Also, incoming implies some to arrive, not here yet.
And no threeway. Yet. Was planning on making a mini story and finally release one. Got several minor avns unreleased due to me not being satisfied with the quality.