I remember some months back there was a news item that Prem will come back in Suman' life and marry her sister to torture her. Well seeing the story develop so far this is what I think will happen. Aadesh wants Chaitali to admit she loves him. So he is pretending to like her friend, Mandy. Chaitali in a fit of jealousy may agree to marry Prem when he asks her.
Prem may also play the emotional card saying how Suman had wronged him. Chaitali always had a soft corner for Prem since she used to encourage Suman to elope with him. So she may end up marrying him to (a) spite Aadesh and (b) to comfort Prem. Only Prem will try to use her, asking Suman to give in to his wishes or he will harm Chaitali. Suman will then be in a fix caught between love for Rajeev and for her sister.