Ok Since everyone is trying to tax their brain cells into working overtime, let me try and put my thoughts.
After reading today's update this is the only possibility my brain could think of at this moment. Most probably Kiran Singhania and Roshni's brother were in love and Bani was conceived as a result but their respective families were against it. Roshni and Jai(he was forced to side with Roshni) probably brainwashed her brother as a result they seperated and her brother commited suicide leaving Kiran all alone.
in steps Nishikant who is in love with Kiran but cannot express it as he is a middle class guy. But now due to circumstances Kiran marries him. It is not mentioned if Bani's mom was happy with the marriage. So this can be the possibility.
Jai and Roshni share the guilt of seperating two lovers and Jai must have broken off with Roshni becoz of the same guilt.
Ok sorry if I bored you all with my nonsense.