Hiding in the closet

Just as mom walks though the door, little Jonny comes running over. He says "Mommy, Mommy. I was playing in daddy's closet and he came in with the lady next door and they started kissing and then they took off each others clothes and laid down on the bed..."
The mother interrupts him. "Stop right there!! Wait 'till daddy comes home!!"

When the father finally returns from work, mother promptly goes up to him and says "I'm leaving you."

The father, bewildered, slowly asks "Why!?! What did I do??"

The mother turns to Jonny and says " tell daddy exactly what you told me today!"
"I was playing in daddy's closet and he came in with the lady next door and they started kissing and then they took each other's clothes off and laid down on the bed...just like what you and Uncle Joe did last summer."