According to the update, Jai makes her promise on their unborn child's life and also in front of God. She told him the truth!! She said " I love you a lot Mr Walia" and "whatever I'm doing to you hurts me more". She was HONEST but she had to go back to being cold otherwise her plan would never have suceeded.
So, please read the update properly! Bani confessed her love (not breaking any promise) then turned bitter again.