The NTR is about sex with other people without approval of the partner, and as far as the gf is concerned she is cheating on MC who (pretends to) not have a clue about her actions. The NTS route (which you can choose in chapter 1 iirc, not chapter 5) involves telling the girlfriend about the MC's kink, so that she knows she's got permission from her boyfriend to fool around.
Just because you want a completely clueless MC doesn't mean this is the only kind of NTR. If this game doesn't meet your preferred type of story, simply move on. It won't change from what it is.
Sorry but no, NTR is when the girl have sex at boyfriend's back without his concent and when the MC NEVER know what is happening, in the moment that the MC know what is happening have 2 ends:
1) the MC cut his relationship with the FMC (Girlfirend/wife/between others).
2) Recognice he like when is happening and start to enjoy it (NTS).
In other words, no, this game isn't NTR in the moment that the MC know what is happening, even if he try to "play dumb" like he said in the game, isn't NTR because he knows, the thing with NTR is the secret, the unknown what is happening, in the moment that you remove the "hiden/secret/uknown" you eliminate the NTR of the game, and is worst if the MC enjoy what is happening because is more NTS than other thing.
If you want to ignore the reality is your choice but, the reality is the reality and the reality is, this isn't a NTR game.
Other games handle this with:
FMC PoV or in the case of games like this, an app to watch what is happening with the FMC without the MC know what is happening (for example putting a black barr in the FMC eyes, is a classic in any NTR)
Almost forgot, if the Dev call this game NTR and ISN'T NTR (Because even if you not want accepti it, isn't a NTR game) is almost a scam because the game SAY something and IS another completly the opposite... So the dev must change the game or will be a scam...
I mean, if you play the game, the dev say there are two routes:
1) NTR
2) NTS
With some dialogs very well marked to select what route you want to play, if the Dev say that, and make two path, the minimum that I want to see is a NTR path, not a NTS disguised like NTR (And bad disguised because I can know that is NTS almost in every moment xD )