He did not face palm when she said that Pakhi hated her since day one, rather he looked away, but did not nod his head no. I think he was acknowledging it was true as he had done many times before, but also appeared to be annoyed this is being talked about yet again. He face palmed when she said that she is an obstacle for Pakhi and I understand his reaction in light of how he has been reacting in last few episodes, i.e. she cannot be an obstacle for Pakhi because Virat has no feelings for and wants nothing to do with her, so Sai cannot be an obstacle to something he thinks is never possible. Of course, this does not address the overall issue about the fact Virat is, in part, responsible for why Sai thinks this way. It is clear that Virat is triggered throughout this entire exchange after MB is brought up, as he starts immediately with tears and then his emotions take over, as always, and he cannot see what is going on around him and how PK is acting.