He had the plan that he will stick to one girl who's not quiet and calm like Diggy who just sit and see everything happening around her, in contrast she's center of attention in most of the issues that are happening in the house, a girl who's not like Rimi who think that ladki ho to ladki ki tarah rehna chahiye, in contrast she is opinionated, outspoken and say whatever she think is right, but despite being that strong headed and outspoken, she is sensitive too and with tears in her eyes seems like a victim who's fighting all alone with the entire house.
Now if he joins her in this fight with all who're against her then he'll become the hero who helped the heroine of the story. This was his plan i.e Rish-Mandy verses all house mates. He tried a romantic angle with her but when she did not reciprocated in a romantic way then he thought even as friend who helps her female friend is enough to achieve that HERO status. (Reminds me Sid & Mehak of Season 5).
So by following this plan these two could be Top 2 favorites of viewers. And as in some aspects he's better than Mandy, like he's more enthusiastic in tasks (before dairy farms tasks, she quitted many tasks owing to her bad health or after having fight with someone). He is also more entertaining than her (she is reserve and serious type) so there will be high chances that in these Top 2, viewers will choose him as the winner.
But she rejected this offer as she wants to play her game alone that infuriated him and he chose Priya as her replacement, again a strong, opinionated, outspoken girl who is fighting all alone with the entire house and he's saying to her if you cried, I'll punch you.