Ok so i think that Mandhar has been a psycho from the beginning. I think that he must have lusted after Pallavi and found her online and went after her. Her friend Devyani probably found out something and therefore Mandhar killed her. On the wedding night, I think the call must have been from something who might have been blackmailing him or something like they knew about Devyani death etc and so Mandy had to disappear. That is why he disappeared after the crash. Maybe in the hospital when he saw police, he ran and became bechara with this dr ramya.....she probably has something to do with all this as well. Anyway she kept him and he pretended he had amnesia. He was probably looking and checking every day to make sure he was in the clear. Once Devyani case might be closed he decided to come out of hiding. (Somewhere in this whole scenario he has met Ved I think....or had something to do with drug smuggling with Ved which is how Ved knew him)
Ved blackmails Raghav about the whole accident etc and Sunny goes to jail and the story unfolds from Sunny as to Mandhar and Pallavi relation which is when Ved tells Mandhar and he is out to get Pallavi back.
And Ved is helping him I think because he gets what he wants and that is to hurt Raghav by separating him from Pallavi and Mandhar gets Pallavi.
Anyway, just my theory.....any other ideas?