Online Defamation

A businessman on Facebook does not belong to our community but has been advertising that he is our community person. Also, we have his personal page where he writes erotic content in his regional language. There are a number of reports that he uses a lot of fake accounts to get more likes and comments on his posts. Also, he claimed openly that he did sex chats. So, we started posting about this person everywhere with his photos and penname(We dont know his married status/location/phonenumber/original name nor we have any proofs). We made a number of derogatory comments about all the above including his relation with his wife and daughter. We only wanted to warn people about his duplicity and his love for erotic poetry. We have claims from few people that he used abusive language against them in the past for various reasons. He uses abusive language in his personal wall against few people. Can he make a complaint against us for defamation? If so, what is our defense?