Transmigrated as the Protagonist's Villainous Fiancée

The Demon Emperor tells the story of Yan Yi, a fallen young man who has been scorned by everyone since childhood. After his fiancee breaks off their engagement and his sect humiliates him, he devotes himself to demonic cultivation and eventually becomes a great Demon Emperor, repaying every wrong done to him. Xiao Yunmo: I can't wait to meet the protagonist from the start! I'll kiss him, love him, protect him, and cling to his golden thigh. Then I can do whatever I want! System: Wake up. Your role is the protagonist's fiancee who breaks off their engagement. Xiao Yunmo: ? System: You have to bully, humiliate, and torment him, urging him to cultivate the demonic path with hatred for you in his heart, until he becomes a great Demon Lord. Xiao Yunmo: And what happens to me after he becomes the Demon Lord...? One-sentence summary: Every time my fiancee humiliates me, she disguises herself as her twin brother and comes to comfort me. Heh... The protagonist, driven to cruelty and ruthlessness by the split-personality Xiao Yunmo, thinks: He really does need a good fucking. Yan Yi: When I first met Xiao Yunmo, he was frail and flirtatious, dressed in white, gentle, and refined. The red lotus mark between his brows made everyone yearn to win his favor. We grew close, became sworn brothers, and accompanied one another. He was the light of my life. I didn't even dare let myself love him openly, afraid it would sully him. Until I learned that he was also Xiao Yunmeng, the evil, power-hungry person who bullied and humiliated me... P.S. Happy ending, with a love-rival showdown at every turn.