His Highness said it was a political marriage and that he could never love me, and he told me he found his true love and would live for love... but why is that person my younger sister?

I am someone who was told that I couldn't be loved because I was a fiancée for political reasons. I was even gossiped about as a "defective fiancée." However, the Crown Prince declared to me that he had found his true love and was breaking off our engagement! He said that even if he switched partners, since it would be my younger sister, the family ties would be fine, and that it didn't matter if he replaced me. No, he simply fell head over heels when my younger sister made advances toward him, didn't he? I have always had my lovers stolen by my younger sister, and this time too, even though my father told me to forgive him, I could no longer contain my anger and finally...