If you simplify the meaning of NTR it's "Cuckolding", which is definitely the case here. The only difference to other NTR-media is that you (partially) control the decisions of the one doing the cucking. In Anime/manga you can only watch the story unfold.
Just because you control the character doesn't make it any less NTR. The majority of games with cheating-elements in them is basically a game with NTR in it, the only reason people don't see it that way is that in most of these, the cuckolding doesn't happen to the character you control.
NTR or Netorare, (寝取られ, 寝(ne) as in 寝取られ means "sleep", in this case, "the lover's sleeping with someone (cheating)". 取られ(torare) is a noun coming from 取られる(torareru), "have something stolen/robbed".
That's why I find it ironic that some developers state the game won't have NTR but at the same time has the Cheating tag... but I guess the NTR-tag is only used when it happens to MC.