As you stated that is what is means to YOU. Those feelings of a brother wanting to protect his sister and son wanting to protect his mother are part of a natural family relationship and do not constitute cheating. That is not how Netorare is defined though, but rather how you interpret it. As it is defined what happens in this game is not NTR. Part of the problem is with the translation to English. The English language is very limited when compared to other languages because the English language does not convey concepts the same way other languages do. This is one of the best Explanations of the NTR concept that I have found so far:
Top definition
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It's a genre of adult manga or hentai. It should be defined as CHEATING/Unfaithful/Adultery.
It is too often INCORRECTLY defined as "
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". However true readers of the genre know that cuckholding is just a sub-element and a fetish. A fetish where one likes to watch their significant other,
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(usually sexual) with another person.
In
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(
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) however the the a bf/gf/wife/husband Do Not have to make a appearance in the story whatsoever. They often Do Not Ever find out about the betrayal. In some
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the cheated on individual may end up in a situation where they are forced to watch there significant other cheat on them. To go slightly further. Some ntr is known as
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. This can also be defined as Cheating. Except it's from the point of view of the individual stealing away the heart of someone already in a relationship. Once again the gf/bf/wife/husband never has to make a appearance in this type of story.
For the illiterate/
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;
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is just Cheating NOT
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. The individual being cheated on may never find out or even be shown in the story.
A sub-element at best seldom/sometimes used, Cuckholding is a fetish. About an individual's desire/want to be cheated on by their significant other.
Netorare can be seen daytime soap operas. Whenever someone cheats on somebody.
You'll probably never see
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in a daytime soap opera.
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can even be mutually desired in
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relationship.
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The Mother and sister are not Cheating or being unfaithful to the MC at all. Since the definition states that the bf/gf/wife/husband often do not find out, they would never have the feelings so the feelings should not be the source of NTR but rather the act of cheating which is not present without a romantic relationship. The MCs feelings of the situation and being upset can be attributed to natural family bonds that do not qualify as NTR. They can also be attributed to envy cause he wants to be the one they are doing things with, but envy in itself should not be consider NTR.
So let me ask you this, If you see a family member, son, daughter, mother, with someone that is treating them bad and want to protect them from that person, is NTR happening to you?