Okay, since some people was confused. I'll make a bit of bad explanation. As someone who had been into seinen/smut, also researching the matter, this is neither NTR(s). However it is still within cheating category, unless the point of view is focused to the heroines of this series.
NTR(s) works is always involving the protagonist's or third-person's possession for the 'taken' part, not the said person themselves. But perhaps if its the chapter tags, then maybe, because this chapter is from Usui's POV.
As for the whole manga, I can say it isn't since it's already set that our actual protagonist is the guy which got 'taken' here, not the the girl(s).
Also. As some of you may aware, NETORARE(taken away) is where the protagonist's lover got stolen. While NETORI(taking away) is where the protagonist is the one who is taking other people's lover. Well, it doesn't need for the pair to date each other, since it still counts as long as just one of any of the two had a crush or strong feelings towards the other. And it does works both ways regardless of protagonist's gender.