"Deathbed" joke

Jake was dying. His wife, Becky, was maintaining a candlelight vigil by
his side. She held his fragile hand, tears running down her face. Her
praying roused him from his slumber. He looked up and his pale lips began
to move slightly.
"My darling Becky," he whispered.
"Hush, my love," she said. "Rest. Shhh, don't talk."
He was insistent. "Becky," he said in his tired voice. "I... I have
something I must confess to you."
"There's nothing to confess," replied the weeping Becky. "Everything's all
right, go to sleep."
"No, no. I must die in peace, Becky. I... I slept with your Sister, your
best friend, her best friend, and your Mother!"
"I know," Becky whispered softly. "That's why I poisoned you."