A sham is a sham! There is no question of loyalty in such relationships. End of the story. Where there is mistrust you can't expect there to be loyalty. And what EMA? Just because he has feelings for his ex that became an EMA? or is it because he is planning to end it with Pratha once he gets the information needed it's an EMA? He has no feelings for Pratha and vice versa. What's so hard to understand here? And as far as marriage is concerned She is a freaking serpent and he is a human, such marriages anyways don't matter legally much unless its bound by love.
But, cheating can also be emotional, not only psychical. And some people are more hurt by the emotional cheating than by the psychical one. Even friends feel betrayed when they see their best friends giving priority to other people instead of them. And if Pratha is innocent, then making her believe that he loves her it's still cheating because she might fall for his act and be broken when she will learn the truth.
I find Rishabh as a very messed up character who is not what he was supposed to be, and I don't know if it's on purpose or not because with each passing episode I feel that he and Pratha are not the end game... just my thoughts.