Stand-In Princess

I came back early from a business trip and found that my boyfriend was with his best friend. Once she traveled through time, she became a literary idiot who couldn't read a word. In order to help her twin sister, who was proficient in music, chess, calligraphy and painting, break off their marriage, she took her place in the house. However, what others didn't expect was that her sister's fiancé turned out to be a vampire demon who specialized in sucking blood for fun. Wasn't she going to be his dessert this time? No, I have to find a way to escape right away! What a horse? Even though he was just a stand-in, this vampire demon actually agreed to marry this woman "willingly"? Oh my god, what should I do?