I have a question running in my mind..Why did Arjun come back looking for Radhika on his pre-wedding night????
I think it was a sort of last goodbye for him because that was his last look at her before he became a married man.
He also knows once he's married to Sam, happiness is something he's never going to have because of the nature of his mission. The only thing beautiful, unsullied and untouched by anything ugly in his life is Radhika. He's come to see her and keep that sight in his heart. forever...knowing that there will one place there that will forever remain pure because of the memory of Radz lives there.
Also, I think it's a sign of his desperate and unfulfilled feelings for her...like a thirsty man in a desert, longing for water to quench his thirst and running towards the mirage.