Well Misha came first in Pia's life but all her secret and thoughts are first known by Abhay d fact that Abhay knew about Pia's past must b a blow to her more than that it shows that he cares for her more than Misha n in a way she opens to him more than she opens to Misha even if he hurts her she cares for him so i think she is jealous of Abhiya where thy show that they have nothing for each other but know everything about each other