I don't think that Nahar and Tara are having an affair, but I think Tara knows about someone he might be having an affair with and is helping him hide his secret. It might be someone that his family wouldn't have approved of so they had to hide it from the family. And since the family also said they have a secret that they are hiding from Saloni, I think thats it. THey might've found out about it after the wedding happened. The person/ thing in the room could be that illegimate child that they don't want out cuz she can ruin their rep and also cuz it looks bad in society and she won't be accepted.. Just some random ideas.. add your own and lemme know what u think