S3·E39 Khushi Congratulates Arnav

Everyone congratulates Arnav. He, however, stops Nani from fixing the marriage date. Later, while dropping Khushi, he brings up the topic of the anklet. Khushi tells him that he and Lavanya make a good pair. Arnav then asks her to step out of the car. Why does Arnav stop Nani from finalising the wedding date?