beta
So the sister is the spoiled princess of the family that is jealous that her older sister is "trusted" with the future and marriage of the family.. And the fiance is a prick who finds Fl "plain" because she dosn't dress up, act on emotions and is in general a well manerd and well taught lady.
He gets with the sister, breaks the engagement and gets her "engaged" to the monster duke... hoping that she will break character and cry / beg him to chose her.
Yet FL choses to fufill her duty asigned by her father.
Im guessing she just wants away from that shitty family that treated her like a workhorse just because she was born with white hair..
They used the exuse that she was the oldest to force her to work for the family, while denying her needs because she "should not act/ be spoiled because Duties".