Hi there! He's not likely to prevail in any suit because the truth is always a defense! But, you do have a cause of action because he is posting things that he knows are not true. Let me explain what defamation
is and then you can make the determination whether or not it is something you wish to pursue. I
am going to provide you information on both slander and libel since they are so
closely related and so often confused with each other. They are civil injuries
that harm reputation, cause a reduction in respect, regard or confidence, or
cause disparaging, hostile or disagreeable opinions or feelings against an
individual or entity. The laws regarding libel and slander are the same. To
prevail in a defamation suit for libel or slander and recover damages, a person
("Person A") must prove 4 things: (i) another person ("Person B") conveyed a
defamatory message they knew or should have known to be false; (ii) the
material was published (i.e., conveyed to someone other than Person A); (iii) Person A can be identified as the person referred to in the defamatory material; and (iv) Person A suffered an injury to Person A's reputation as a result of the communication.
Typically, before actually filing the suit, you would send them a letter detailing the situation and demanding that they: i) retract all prior defamatory statements made, and ii) cease and desist from making any in the future. The letter usually resolves the issue because people hate to get sued. If you need a template for a letter, let me know.