Didi ke sangat mein Babusahib ka bhi one track mind ho gaya hai...he's so hung up on telling his Imlie wala truth that he overlooks the full scope of the problem he is in. Your problem is multi-faceted Babusahib, so you need to tackle it accordingly.
He has successfully convinced everyone how right Malini is a partner for him, so it will seem jarring for them na that how all of a sudden their marriage is crumbling? He has introspected that he has never loved Malini, he needs to have this conversation with Imlie too. Because he has drilled into her mind for so long that he loved Malini and how she was the best partner for him, toh Imlie might think that he has fallen out of love with Malini because of her. Perhaps that's why she thinks she has come between them? Adi needs to explain to her clearly that Imlie didn't come between them...and explain his feelings for Imlie v/s Malini as AY said already. Well at least today he told her firmly not to interfere between him and Malini, that's a start!
He's already introspected that his relationship with Malini was based on comfort and convenience but he needs to introspect also on the fact that he never knew Malini at all, and she didn't know him either. They were always incompatible... He needs to understand all this and explain it to his family and Imlie. I understand that right now his only agenda is telling his family about Imlie truth and he's laser focused on that, but he needs to wake himself up to the full scope of the problem he is in. Otherwise, this will bite him in the behind later too like his decision to bring back Imlie did. It's also very important that he has this conversation with his family because if he doesn't, Didi will use this point as ammunition later to play victim that she was always devoted and loyal to him and he strung her along for 7 years and then fell out of love with her overnight. Which simply is not true, the truth is he didn't understand his feelings for both Malini and Imlie for so long and that's why he made so many mistakes. He needs to explain this to his family before outing the truth, otherwise Imlie will have to bear the brunt of Didi's ghatiyapanti.
But even then, I don't think Imlie's guilt will go away....Malini needs to insult her Mom & SK for something to click in her. I hope truth is outed before it is revealed that Malini is her half sis, because after that...well let's not try to imagine what happens after that.😆