Arnav did notice how she cared about despite him telling her to stop several times. She didn't care about his anger and helped him. She stayed up only for him.
We know Arnav thinks Khushi is a betrayer. He has gotten many hints so far which should make him re-consider the misunderstanding. However, he hasn't. Perhaps because of his ego. He doesn't want to admit to himself that he could be wrong or he thinks that she is just fooling hi again with her love like she did in the past and he is not about to let himself fall in that trap again.
"Jaltay Pay Namak"...Ok, I guess this is not the most appropriated statement for the situation but that is what crossed my mind after Anjali reminded him of what Khushi said. As Khushi had said "Aap ka Ghamand jal raha hai". It felt to me like the reminder of Khushi's action worked as the namak on his jalta hua ego. Despite not wanting to, he is starting to question himself over why she cares for him and Anjali's words only reinforced that point.
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