As you entertained the other guests, your wife took him to the bathroom.
When your wife told you that your sisters were taking her out for her birthday, you did get a little worried, because you knew that they had been talking with her about cuckolding you -- but you still are shocked that they have been successful in their efforts -- and you're not sure how to react, but you do know there is nothing you can do to stop it and that your relationship with your wife is about to really change.