It's funny because it's totally possible to avoid NTR. The game's biggest hookup for the NTR is even listed. For example, when Nicole is kidnapped, she mustn't scream, otherwise it's NTR.
If you choose to live with Tyrone, you have to show your love to Nicole, otherwise she will go to calm down her ardor with Tyrone (at least for now, it's just words, there are no acts).
In fact, if you are choosing the path to NTR yourself, don't complain that there is.
The only act that is impossible to avoid is the rape of Nicole by Robert, but it is not NTR.
It is, I think, to add a possibility that Nicole is pregnant with Robert whatever the chosen route.
After all, we can impregnate several characters, why is it wrong that our wife is impregnated by another man?