Him and FL met at a masquerade ball, so everyone thought she was her elder sister, who everyone adores. FL's parents spread rumors about her in society because she's going to die in a year, and they didn't want to spend time mourning (?) over her death while her brother is succeeding the duchy. Anyways, FL is extremely sheltered, and goes to masquerade balls in the name of her sister to meet with ML, because they fell in love. Fast-forward a bit, and he gets engaged to older sister, who he thinks is his lover, and is ecstatic about it. He meets FL at the house while their engaged, and instead of recognizing her, like a person who actually loves his lover would get, he feels uncomfortable with her because of all the bad rumors about her, which he chooses to believe, EVEN THOUGH HE FELL IN LOVE WITH FL BECAUSE SHE DIDN'T CARE ABOUT THE RUMORS ABOUT HIM!!! Elder sister and FL swap on the day of the wedding, and he is PISSED. He basically acts like a megabit*h to her, and she acts like a villainess back, which I think is because of resentment for not recognizing her as his lover. Oh, and by the way, this entire time, she has a terminal illness that she's hiding, so he's doing this to a sick, weak person.