It is NTR, because the character is still in the game, you cuckold
I'm not into NTR, but a little NTR explanation for those who never cared to look it up :
-Netorare : Person of love interest being stolen, without consent or knowledge about it, and that the said character is reluctant at first
That's the one you find everywhere, and people think NTR is only that
-Netori : it's basically the same, but it's you as the MC who cuck others girls (and I bet most people who don't like NTR don't care if you're the one doing the stealing in a game)
-Netorase : it's one more time more or less the same, but here there's consent about it
In the 3 cases, that apply only to a point of interest, if you don't develop a relation with a character, it would be wrong to call it NTR, 'cause it's not ^^'
And I'm a fan either, it's kinda cliche, but at the very least I did my search on it, 'cause I'm not in the bunch of people who talk about a subject they never bothered to inform themselves on
So long as the character isn't a point of live interest, or that you don't wanna go to a relation with it, it isn't NTR, properly speaking, NTR is a word used here and there meanwhile at least 30% of the time it isn't even NTR, people just tag it because they have no clue, and to get more view around people searching this tag