Vasu took advantage of Ragini's vulnerable state and instigated her against Sadhana. Vasu knows very well that Sadhaha can never be jealous of Ragini's happiness as she married Alekh only for Ragini. But by making Ragini against Sadhana things became easy for her. She emotionally blackmailed Alekh by telling him see how Ragini is suffering. But Vasu will pay a heavy price for this.
So moral of the story is "United we stand, divided we fall".