Well, yes, that is, at it's core, what NTR is; your wife falling 'in love' with another person. There are varying degrees, so yes, you can have a NTR story where the man whose wife is 'stolen' permits it or allows it, usually out of his love for his wife, but a story where the woman does it against the man's wishes is equally NTR. If the wife/girlfriend allegiances don't shift from her original partner to a different person, then it's not NTR.
I mean, I don't disagree that this story is clearly on the humiliation and degradation side of NTR, but it's also a perfectly valid NTR path, and as bleak as it is, I don't think it needs to be fixed. I also enjoy stories like Seeds of Chaos, but I think there's room for both.