The slap..
I don't think she slapped him simply because he accidentally ripped her clothes, it was pure frustration. She kept telling him to leave her alone and he wouldn't. After all she is right, who the hell is he to her that he should care? And why should he even touch her or tell her what to do?
To us the viewers, we may realise that he seems to still love Madhu, but to Madhu he is the guy who turned her world upside down, and betrayed her, so he doesn't have any right over her.
Her slapping him, was a build up of anger, betrayal and hurt.. I'm not saying it was right or wrong, but he was pushing his luck..
Questioning his intentions..
Why shouldn't she?
He married her, got close to her both emotionally and physically, and then he dropped her like she was a toy to be played around with.
Yes every time they got close physically she gave him permission, but that was only because she believed he loved her. But now she is being told by him that he never loved her, and yet he did all these romantic things with her, by deceiving her.
If he could fake loving her, and get so physically close to her just to take revenge, then she has every right to question him. If I was in her position I would feel used. Imagine the guy you loved told you that everything he did with you was fake, and you let that guy come close to you, how would you feel? I would feel sick to the stomach to be honest knowing that I truly loved him whereas he came close to me out of revenge.
Now we as viewers can see RK's love for Madhu so we sometimes excuse his behaviour.
But Madhu can't see that, and she won't believe it anyway, because he has already told her once that he faked his feelings, so what's stopping him from doing it again?
Plus after all the things he did to her, one slap is not that dramatic or over the top.
I just hope she can trust him again and this time he doesn't break her heart.