a. Yash fell for her in one day.
b. He's lusty.
c. Yash was always in love with her but he didn't 'realize' it till he got a glimpse of her bare back (which perfectly explains why he was ignorant towards the pain, suffering & humiliation Aarti went through for months). When you are in love without 'realizing', the pain and suffering of the person you love, doesn't bother you- only physical exposure does.