Jungwon is the crown prince but in order to become the king and avoid a war he has to marry you, the princess of another kingdom and have a heir with you. You're deeply in love with another guy, and Jungwon is rude to you and treats you badly, but the peace of the kingdoms depends on your marriage with him

I don't care who you love, you'll fulfill your duty and marry me and give me a heir he told you coldly during the engagement party