I got to watch the epi again and was paying attention this time... 
I know a lot has been written in this thread and some of what I say may be unpopular or call me flipbaaz... I am just voicing my thoughts as it is an open forum. We all have our perspectives on life and things in general and it colors our view.
Here goes..deep breath.... 😆
Mithi saying suhaag cheen lees... 
When she had ONS with Dev, it was out of love and she must have been young too, who succumbed to her emotions at the time. If she had an inkling that Dev was already shaadi shuda with a child, she would never have gone ahead with it. That is her moral fiber. Then he left and never once returned to check on her, she waited and bore the taunts silently, raising her daughter to be strong n independent. When she found out that he was already married, the small flicker of hope in her DIED for GOOD, saw him really for what he was. Was able to dismantle the mandir she had of him, was ready to move on alone, with her head held high. She also realized the true worth of SK (knew it before but was ashamed of her past) and decided to fight for him. Her bg and village society did not give her the confidence to pursue him as he rejected her post the Dev visit. A woman who has been broken for years, finds that the one person she relied on also keeps her at arms length has to be the last straw. Her personal principles n morality is labeling her guilt on having a ONS with a married man..hence her genuine heartfelt apology to Anu who was BLIND to her anguish. Both Mithi and Imlie have this pride of coming from the land of Sita Maiyya where women are revered, held to high standards.. the fact that they consider themselves unworthy of that worth due to their 'mistake' or cannot take another woman's suhaag is a sin, irrespective of being the first wife or not. Both are tainted by the same brush, ashamed of their weakness, reminded at every turn. 
Imlie feeling the same and calling her DD her bandhan, not just behen speaks of the above. It is a hard and bitter pill to swallow as the discovery of her birth has shaken her to her very core. 
Coming to Aditya.. now and his convo with Rupi --
Here is a man who is grappling with the enormity of his own mistakes and the mess he is in. He is blaming himself for this and he is a stickler for truth. He is taking steps to fix the mess, his love for Imlie, his guilt over Malini, hiding the truth from his family are all taking a toll on him. He is working towards revealing the truth to his family with a single focus and ready to deal with the fallout. He has experienced the gutan when Imlie was absent before he realized what his feelings were and now that he has acknowledged his love, is even more afraid of losing her. He saw the effect of Anu's words on Imlie, the truth of Dev being her father and the product of an illicit liaison. He knows her all to well about Dd, the affection that she has for her.. ( it is too much Dd jaap n Drama by the makers) Imlie is much stronger emotionally than him, who has walked away and that is his deepest fear. The man is emotionally drained for having held the truth from everyone. After consoling her, the man is shaken by what he witnessed and is relieved to share his fear with Rupi didi for once. Nishu just got married and can't share it just yet. He needs all the forces on his side to help them overcome this. Plus Rupi has been from day one of when Imlie arrived at the T house and has been encouraging Imlie. 
What can Rupi do, I mean she has not moved on in her own life and is in a limbo. She has protested and keeping in line with her character. What will she do now.. let us see what is bestowed on us by the makers. 
Could this have been written better and executed better, yes absolutely. I am just writing from the POV of the characters.
Ready for the brickbats coming my way... 😆