You know, this is actually kind of funny. Usually in NTR plots, the cucker is usually an asshole, douchebag, etc.
Yet here, the dude's trying to show respect and be genuinely friendly, is looking for a long term relationship and the girl is a bitch. The bitch type, not the horny type.

Imagine an NTR where the dude is all round a good guy but the girl is an asshole.