Because he is actually not a good person. Someone who gets engaged to someone else but keeps you around and blatantly ignores your affection is a cruel person- and I don't care if the engagement is political because the Princess is using it to create more distance between them (which she should as she is engaged to him and he agreed to it). Owen is refreshingly normal despite everything. Not great but shes not great either so they're both learning. Honestly- this manwha is quite refreshing in terms of the realisim.

Why does she feel the need to hide? They aren’t even together, they never been together and that man has a whole fiancé. She looks foolish trying to hide her relationship from him.