@Kizuro well, if thats what you think netorare is then you are wrong.
Cheating in japanese is "uwaki". Netorare (just as netori or netorase) carry the nuance of "taking", in other words, netorare its not about cheating but about someone you love being taken away from you. There is no need for that someone to be in a relationship with you to consider it "netorare" (it can be a friend you love, for example), BUT you need to be in a relationship with someone else to consider it "cheating". Do you understand the difference?
So in this scenario this, obviously, isnt netorare because no one is taking anyone away from anyone else. Its simple and plain cheating. Its still bad tho, but shit happens.
Problem with NTR nowadays is that the misconception about what it means has taken such a deep root in the community that its impossible to fix it at this point (just like how the majority of the community think that "doujin" means "hentai manga" LOL) and since the NTR hentai genre is somewhat hated by those who dont like it and people think that cheating = NTR, whenever there is cheating in a series people automatically project their hate of NTR hentai against the series and the comment section became a sea of cries.