You first need to tell your husband , that is the first thing you must do .
Then both of you need to go to the police and see if they can charge him for this , maybe they can set up a sting like they do for people who blackmail for money .

This problem wont go away so you have no choice but to do something and if you sleep with him he will more then likely be video taping more videos and blackmail you forever so it must be stopped .