You may be able to sue her for defamation. Defamation is the pubic (which means to even one other person) making of false factual assertions (so a statement that you had an affair, which is a factual assertion or statement, would qualify if it is untrue) which damages the other person's reputation and/or makes others less likely to do business with that person (which the statement that someone had an affair and cheated on his wife would tend to do). You may wish to consult with a personal injury attorney to determine, based on the circumstances, how strong your case is, what it might be worth (i.e.  how much you may be able to recover), and also what it might cost to pursue the case.Remember: truth is not defamation, so if you have had an affair and she does obtain evidence thereof, it's not defamation.