What revenge is being had from that definition, the MC get's netorared and that's it. Netorare has to do with the emotional turmoil of the MC and their LI being stolen from them otherwise it's just regular cheating. Or are you thinking of netori?Here is a defination of NTR according to this very same forum as quoted by Mr.BLasKyau above.
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so we can't actually agree to disagree when that's what this very same forum defines as NTR. Ignore what those Japanese games show man. those are really really filthy. try some Western ones. and you will see the difference.