when rimjhim had cancer, malini had married avinash. she hated rimjhim and wanted to instigate rimjhim's daughter megha against her. In a bomb blast, avinash had lost his memory, and malini's arm was burnt, but the world thought that she and avinash were both dead. rimjhim one day discovers that avinash is alive, but he acts all weird (with amnesia) and doesn recognie rimjhim and his family. at that time, shweta pretends to be avinash's wife. malini is still alive, but she hides somewhere and sends shweta (who is her cousin) to live with avinash. shweta gives him drugs to make him more ill and instigates him to avenge his own family for some reasons. rimjhim finds out that malini is alive, so after a huge series of episodes, rimjhim shoots malini to death. that's y megha is shown to hate rimjhim so much, cuz she took malini for her mother. meanwhile, as shweta is living with avinash, avinash takes shweta to be her real life and shweta gets pregnant. rimjhim helps shweta get away so that avinash doesn find out. but shweta schemes and puts rimjhim to jail for murdering her cousin malini. avinash gets him memory back and is sorry for everything he did under the influence of shweta and malini. so, after the leap, when rimjhim comes out of jail, shweta comes back to claim her rights on avinash and her illegitimate children.
hope that helps!