the first one could be to prove to kala that he's better than her at her own game. kala wants dutta's marriage to be broken. so what does kishore do? he goes one step ahead and not only gets the marriage broken but dutta's heart too. so that dutta not only doesnt marry supriya but wont think of marry any girl in the future. all this without any bloodshed. badi hasti had written a note to kala telling her that the sisters' plans are silly and his plan is the smart one.
but here the casualty would be dutta and what would kishore get from dutta emotional breakdown? and here comes the second motive-jealousy. Kala and sudarshan are shown to taunt kishore for not being like dutta. kishore knows he can never match dutta in terms of wealth and power that he commands and thus never gain wife's respect. and which man would want that. so here comes jealousy. if dutta is emotionally broken there would some kind of satisfaction in it as eventhough dutta maybe powerful but emotionally he is as weaker than most men.