What made him do this?
Is it to make Abhi feel he is doing something wrong when Pragya will admit love or marry (fake) Purab?
Abhi wasn't upset about the affair itself. He even said he would not have tried to stop them. His issue was they hid it despite him asking several times. He will soon get over it I guess.
But then what is Purab's motive? Is he trying to get back at Taaliyah? But, how?