What can I say? The HOTNESS would be enough to fall for!
Kushi was attracted and repulsed by him at the same time in the start! I think even NOW she feels that way sometimes... BUT she knows the Arnav in ASR now, and THIS is the person she has genuinley fallen for!
He is handsome, sexy and passionate! Underneath the stern exterior he does have a warm heart (like his mum said in her letter). He loves his sister and is loyal to her! He showed his big heart when he was nice to that little kid at the temple and then paid Khushi's Dad's bill. He was even very respectful to Khushi's family!
He is good to his family. (Cares about them, even puts up with Mami).
Need I say more?