From some time we see that Kunal is trying very hard to put up this face "I hate You" in front of Siddhi and trying his best to continue stupid charade. But few minutes he spends with Siddhi and his defenses get very weak. So many times he exposed himself but realized it and stepped back. We have pani puri scene, party scene-dance, blouse button scene and cornering Siddhi in office.
But yesterday he failed big time. Tried to keep up his lie with power under love-jealousy. He tried to put good enough effort but he got so vulnerable at the end he blurred out "Meri Siddhi". It appears he doesn't realize what he said or how pathetic liar he is in front of Siddhi.