It's a parody after all.
She is not you girlfriend. This is not mentioned anywhere. Yes, she loves to fuck with your character. But it was not hidden that she loved Harry from the very beginning.
So, while it's not hidden that she has a crush on Harry, Hermione also wants to impress Harry and Ron, yet she is fully romancable and has no cheating if done right according to you, so I don't see how we are expected to know Ginny's route will be any different. I genuinely don't know how a player would be expected to know that her route doesn't lead to an actual relationship with the evidence the game gives.
Also, whenever my character saw them together in the park she felt genuinely betrayed and jelaous. She was genuinely upset. Those are the textbook emotions for NTR. I'm not saying that this is an NTR focused game, but I genuinely don't see how this game shouldn't have the tag.