He (according to him ) remembers everything that happened in the hotel room that night when he was in sub conscious state (according to us )but does not remember his conversation with Sidhi when he was consious and fully aware of what was happening.
He remembers kissing Sidhi but has forgotten sidhi kissing him.
He remembers being rude to his father , behaving badly with his family in drunken state but has forgotten Sidhi taking care of him when he was passed out..I guess at least when he woke up in the morning he would have understood
He remembers going to the party to save his "friends" life but has forgotten that his wife tried her best to stop him from going to the engagement.
He remembers Sidhi not telling him about where she goes, whom she meets but has forgotten that he himself told Sidhi that he trust her completely so does not want to know where she goes , whom she meets.
After so much pain Richa has caused him (in the past) he remembers to trust her, believe her blindly but due to one or two incidences he has forgotten the trust he had on sidhi and is doubting her intentions.
He remembers what she has done for his family but has forgotten the incidence when she told she did it for him not for the family
He remembers the authority he has on her , the right he has on her to scold her, shout at her ..but has forgotten she has equal right on him.
Well Mr Kunal Chopra hats off to your memory..wish I also had such a memory where I could only remember what I want to and forget rest.