I think Pallavi cheap tactic is going to cost her big time.
Now she has successfully planted in RR mind that he can't be a father, which RR will take it seriously.
It seem the exGF is a positive person, and my assumption is she left him due to some dosh but lied to him about him not being rich etc. So now the truth will be out, the difference between them will be cleared and they will be friends.
But because of his infertility, he wouldn't want to spoil Pallavi life, so he will ask Eesha help to act as his lover, getting close to him etc, in order for Pallavi to hate him and leave him.
Now, whether Pallavi will get to know the truth why RR is doing this or separation is on the way, that is mystery.