Not quite. We want the terms we use to have meaning and refer to specific, clear ideas so that when communicating we are understood. (this is to say language is a game in which we follow public rules to be mutually understood). English already has a term for what happened here - rape. Your specifications of the lover not knowing about it or not is not particularly relevant to the conversation. There is no ambiguity or lack of clarity here. The problem arises when the term "NTR," which used to refer to something specific, is broadened and used for any violation of purity or loyalty. (In the modern day someone would call rape NTR even if the girl was not in a relationship yet.) This causes problems in that the original term ceases to be useful and becomes kind of a tool for rhetoric - by muddying the waters much like philosophers do, they can better vent hatred while disguising their own insecurities. It is this misuse of language above all else which disturbs me. As the world's foremost leading expert on NTR it is deeply bothersome to see the term itself get fucked up the ass so immensely that it now represents all the evils of the world. And the tag subsequently meaning nothing. It was much more respectable back in 2011 with Elf's seminal release of Gatenkei back before it became a boogeyman in this nature.
(All this said, corruption of language is in fact the natural state of things. As things go I wouldn't be surprised if in 20-30 years "rape" as a term was all but entirely depreciated and everyone just says NTR in all contexts.)
