Arnav's feeling are much more developed than Khushi. It will come to forefront when Khushi stops coming to RM (via marriage plans) - a case of absence makes the heart grow fonder.
Khushi has yet to develop a liking to Arnav. Maybe it is Arnav's constant reminder of her "aukat", she doesn't have any romantic feelings towards him at present. Had she any, she wouldn't be grinning in the precap.