LB, It is a discussion of the blemishes for which a woman can refuse yibum. Even if her husband had the same blemish she can say that her husband was worth putting up with it but his brother is not. As for love changing, you are confusing the Western idea of love with the Jewish idea, which is having two halves of the same soul and thus wanting to give to the other, The Hebrew word אהבה is related to the Aramaic word הב (give).
DY, what will you answer when you are asked if you leard דבר בתוך דבר?