Putting all logic aside....
My feeling is that Anupam has something to do with Sneha - as we don't know what actually happened to him Sneha may even be with his family where she was the cause of the pamnivi split - That would make such a good fanfic!
(no stay focused here)
It can also explain Shivi's secrecy about things.
If the Sharma's think Sneha is dead, shivi would have told them, she knew what was going on at the time and can be angry with Bajaj for taking Prerna away before they found Sheha and possibly even blocking all attempts at reunion.
That would then explain his distancing from Kukhi - so that she and Prerna share a close relationship, knowing it is all that will keep Prerna with him if she found out the truth.