Dog and The Master

Binoy, a big businessman in the town, was leading an unhappy married life and he took to drinks every day to get rid of his worries. His trustworthy dog, Bittu, accompanied him round the clock and he loved to be with him wherever he went and that was a great source of happiness for him.
On that night he went to the bar with Bittu and had drinks above his usual limit to tide over the mental agonies. As he was unable to walk down to his car, barman’s help was sought. That person offered to drive and leave him at his residence. On the way, the car was stopped and Binoy was dragged out and stabbed him saying, he was doing that as he was paid by his wife to do so and ran away.
Why she did so? Was she having a paramour?
Ultimately what happened to that couple?