The immediate hate for the prince is a bit overboard. We already know from the FL’s perspective that he was previously engaged to Cecilia but she was assassinated by the duke, so she had to marry him. It’s obvious that, even without the spoilers of him loving the FL, that if he hated the FL it would be justified. I mean, she came from the house of the family that killed his fiancé, and was forced to marry the FL most likely for political reasons. I can understand her trauma for being hated by him, but it didn’t appear that he did anything but express his distaste for her. It actually makes sense if they fall in love (again?) since the only bitterness they had in the past timeline was apparently a misunderstanding. They never had any actual discord between them, other than her traumatic memory of him hating her (which she shouldn’t have been surprised about).