What happened was that Rajesh and Putul had been in a relationship for a while. Putul used to visit Chapra for her examinations where she would often meet Rajesh, and the two had fallen in love. But since neither of them had told their families about their relationship, eventually, Rajesh's marriage was fixed with Rinku.
On the day of the wedding, it became unbearable for Putul to watch Rajesh getting married to her sister, so she called Rajesh mid-ceremony and threatened to jump off a building if he went through with the wedding. Rajesh immediately stopped, and revealed everything to the families following which a ruckus broke out at the wedding.
Eventually, police had to intervene and they asked the two families to sit down and solve the dispute together. After much discussion, the families finally agreed that Rajesh and Putul should be wed.
(With inputs from India Today)