After my intial shock by watching the last part of the 5th July episode!! I realized that what Aman is doing out of a sudden...by declaring that he and KK are to be engaged..!!might seems shocking to some..but actually he is helping Rahul!!!
He is helping Rahul go full force after KK..Aman knows how much Rahul loves KK..specially after the hospital scene..so what he is doing is intentionally done. This way Rahul will realize KK is not happy. She doesnt want to marry Aman she loves him..he will never keep his promise to KK by marrying Naina!!