You don't have to provide him with an explanation whatsoever. Stop discussing it with him and refer him to your Lawyer. He keeps at you because he is hoping you will feel sorry for him and back down. Don't. If you feel that strongly about the date then close the discussion.
~ swl
Look not mournfully into the past. It comes not back again. Wisely improve the present. It is thine. Go forth to meet the shadowy future, without fear. {Henry Wadsworth Longfellow}
