In the KC episode it had finally dawned on Ayesha that Milsi does not want to be with her even if he is not with Prachi. Milsi had earlier told that he wanted a divorce not for himself but for Prachi's happiness (I think it was his birthday). He has also been repeatedly telling her that though he knows she wants him he can only offer friendship. In the hospital he told her that Prachi resides in his heart and there was no room for her. But Ayesha was not willing to accept his words. She thought that Milsi was under some illusion and Prachi has just cast her spell on him. Once she seperates the two and ensures he hates her, then there will be no problem getting back into his life. She then embarked on her grand plan of unravelling the baby raaz to achieve her goal of getting Milsi back.
Unfortunately for her, Milsi just showed her her place on KC night. He categorically refused to be seduced by her and told her that he values their friendship to belittle it by a ONS. He also said that he cannot play with her heart since he cannot offer what she wants, i.e, love.
How is this incident different from the many in which Milsi tried to tell Ayesha they cannot go back? This was different because this happened after Milsi told Prachi he hated her and displayed his anger and disgust in her in full view of Ayesha. It happened when they were alone with all the opportunities of the world. It happened when Milsi still thinks Prachi betrayed him in the worst possible manner. It finally hit her that even if Milsi hates Prachi he still will not accept her. The shock this realisation had on her was there to see. Yes, she still blames Prachi for it. But she knows she has lost Milsi forever.