I think I know why. I could read his face and he was like o my god not again. He must have hoped Tanya really did not do something stupid to hurt Nandini infact he asked Nandini the same too. I dont blame him for that reaction because of endless arguments, baseless accusations for last few months. It is a shame that this was to occur but it was solely Tanya's decision not Karan's. He did not tell her to die did he?