This story line in Kaajjal seems like a copy of the movie Mohabbat where Akshay Khanna does the same thing... he dies and then they find his humshakal, who turns out to be the same guy.
In my opinion this Raju person IS Dev, and not his humshakal. This story has to drag, getting Dev and Kaajjal married would be end of the story, thus this new concept! Let's see how this goes.