I too recommend going to the police, and by extension telling your husband. It's one thing to have cheated once and had pics of you, but each time you submit to the blackmailer you are getting deeper and deeper in a hole you might not get out of. I don't know how you got into the situation in the first place, but dealing with your original discretion early (as in now) pulls the blackmailer's weapon away from him, meaning it can't get worse.
At one point you have to trust both your husband and the police to accept what you did and protect you from further harm, but that truly requires you to accept the responsibility for what you have done.

Good luck.