Karan is hating Nimrit as he thinks its her who has blackmailed his sister..some photographs .video of her intimate moment with her fiance was taken in a hotel room...the blackmailer was asking for money or else the video will be on the net..its because of that karan sister commited suicide..
Thats why karan is marrying Nimrit to get his revenge from her.
On the other side its shown Nimrit is innocent ..she has nothing to do with it..in fact after taking help of an IT technical support Nimrit got to know its from Amrit laptop that a fake account on her name was created and these mails were sent to karan sister. in mumbai.
Now to protect Amrit she is sacrificing taking the blame on herself.