I feel the person behind Kasturi is neither Robbie nor Raunak. It is somebody else. It cannot be Raunak, because if it is him, why will he walk so slowly and delibrately towards her at the end of the episode??I would think he will rush to her and try to calm her down. And as far as the dress is concerned, I think that's the creative team confusing the viewers to build the suspense.
So it is somebody else who wants to interupt their honeymoon (other than Robbie) and will say something to Kasturi. And while they both are having some argument, I feel Raunak will reach there and then dono mein haata-paai hogi and Raunak will get hurt. And then this will lead them to thinking that all of this was organised by Robbie Sabharwal.