Legal Question in Family Law in North Carolina

I suppose you could but why would you want to?. In your question you use the words 'before you are divorced' which leads me to believe that you are getting divorced. If so, it seems rather pointless to send a cease and desist letter unless you are planning to try and save the marriage. If you are planning to save the marriage you should rely on your husband to end the affair not the mistress. Otherwise, if the marriage is not salvageable and you know you are getting divorced, all a cease and desist letter at this point would be is basically a sad pathetic attempt to assert your will on the mistress and your husband. You should likely consult with a local attorney, if you send such a letter yourself you need to be very careful about the wording so that it can not be construed as libel or threatening or you may end up being the one who is sued. Best of luck.