Hey! Thanks for the feedback. I believe the issue here comes with your interpretation of "Purity," or what a "Pure" playthrough means vs. the way I'm using "Pure" "Lust" and "Dark" narratively.
In the context of the relationships you can form with each character... Purity means slightly different things. Sometimes it means no romance, but that's not always the case either.
With Olivia, currently the only way to get on/stay on her "Purity" path is through romance. While this might seem odd on the surface, keep in mind that I treat every character as if they are their own person, with their own feelings, and they will therefore have different reactions to the type of (or lack of) relationship you desire with them. In Olivia's case, which path you're on is determined heavily by the way your actions make her feel... and she's not happy if you reject her, regardless of your previous interactions.
While rejecting Olivia leads to her Dark Path, and there's currently no way of getting around that -- even "dark" players are never forced to do anything they don't want to and you can also steer things away from that path in the future. Players will be given the opportunity to "fix things" and the MC can correct his mistakes with her... namely, the way he sort of (intentionally, or) unintentionally leads her on prior to the rejection.
Now as for giving players the option to express only platonic feelings for her initially... something you should consider is that while I do try and give players a lot of control, it's impossible for the main character to not have some autonomy/his own feelings and behaviors. Olivia is written to be a lot like Gracie, and therefore when the MC first meets her, he indeed feels romantic feelings for her, and there's no way around that either. Sorry if that's not ideal for the type of playthrough you were going for! I definitely get where you're coming from and understand that the MC sort of... messes up by admitting things he feels initially.
If you want my advice... it's not to treat romance with the characters as a "negative," even if you suspect they might be leaning more towards the taboo. My recommendation would be to romance Olivia fully, and reject her as little as possible if you desire the happiest/best possible outcome with her.