this relationship is toxic as hell, making it seem like you're in love with someone else and saying that you're going to annul your engagement just for the other party to admit that they love you, is manipulative and its not healthy at all. If this story were to be serialized or continued, I'm sure there would be more scenarios where the prince does something similar for her to admit something. It's kinda like gaslighting, though I'm not sure if it could be described as such.