Shiv had fallen in love with this unknown girl at the very tender age and he has made a dream world of his own with this mystery girl and as he is stubborn he refused to let anyone take her place in his life,if he is not destined to meet this girl then he refuses to marry anyone in his life and this is the root of all problems in his life.
As Nikhila wants him to get settle down she must have consulted Guruji and he after seeing his kundli must have told her that Shiv has kundli dosh.so Nikhila planned on this chaal and told Shiv that if he marries someone for a year then he is sure to get his dream girl and after his first wife gone to heaven he can settle down with his portrait girl,and shiv who is ready to do anything(his khushi.....remember)for the first love of his life,gets trapped in all this
But Nikhila is more cleaver she has planned to present Ippy as the portrait girl after Gauri,s death because she is her friends daughter and must be inheriting a fortune.And guruji is game with Nikhila and own dear Shiv is just a pawn in her mothers hand.
I hope i made some sense pls tell me if i need to rattle my brain more