Last night she felt that she has lost Kunal, you'd think that Mauli will take Kunal's shoulder to cry but Kunal is not that Kunal for her anymore, she had that feeling of losing him, that sense of being near something that's not yours, so she went to the person who's closest to her after Kunal and that was Nandini, she cried her heart out but little things she was doing like lightening the moment by smiling and changing subject shows that she wasn't even able to tell Nandini everything she was going through but she had to release something and she did.
I would say it again that Kunal and Nandini keep saying or pretending that they care about Mauli but they don't and it's not their responsibility to take care of Mauli, but at least stop saying it, you can't have the cake and eat it too, especially Kunal after that bathroom crying scene he didn't do anything to stay away from Nandini, he did everything to make sure Nandini loses it and tells him about her feelings, what was he thinking to gain? What did he think Nandini will do after she tells him about her feelings? He was constantly triggering Nandini to accept her feelings in front of him and of course there was a facade of his love for Mauli, he pulled the cable plug so family won't see what he and Nandini did, wasn't it just a hug? What's wrong with a hug? And he was constantly looking at Nandini, Mauli was crying for him and he didn't even spare her a thought, then he kept looking at Nandini's bedroom door, it's clear he doesn't want to hold his feelings, he just wants to keep the mask of a good man on his face.
Nandini knows that Kunal loves her and she fell for him seeing how good a husband he is, I remember when Rajdeep brought a girl home that was the first time Nandini has said something along the lines of her dreams of marriage being broken, now when Kunal is in love with her, cheating is alright because Kunal loves Nandini not any other woman, if Nandini had seen Kunal will any other woman than Mauli, she would have told Mauli because she cares about Mauli, like Mauli told Nandini that Rajdeep was hitting on her, if Mauli was as fickle she would have kept relationship with Rajdeep and would not have told Nandini about it but she's not like that she saw that Rajdeep was not good for Nandini and she told her, but Nandini is not telling Mauli about Kunal's true face so I don't see where is the love or concern for Mauli, it's just plain selfishness and it's not wrong to be selfish but don't be so heartless to betray someone who helped you shaping your life.