Yeah good job in nitpicking what i said. What i meant is that Olivia would told MC that his GF is asking these things also people here are constantly saying how the girlfriend knows it is his kink and that's why she is doing it so what is it ?
Except it doesn't make any sense for Olivia to be someone who the gf seeks advice from. Not only the gf dislikes Olivia and mocks her, but Olivia doesn't know shit about relationships and cheating. She didn't have sex yet, and is actually the person who is asking others about basics of relationships, and ends up getting influenced by them, MC included. Not to mention she doesn't even appear in MC's phone until middle of the story.
The girlfriend knows it is MC's kink if you choose to tell her. On the NTR route which you talked of specifically, she is unaware because MC hides his kink from her. That's what makes it the NTR route. She knows it on the NTS route, which activates if you do consent to Sabrina telling her about it.
(the point is that providing this sort of info in this kind of game isn't really as simple as you thought)