Spiteful Landlord threatening to sue me for making true public opinion comment about my experience living in his property

I lived in an apartment complex over 5 years ago. The rental management property and its owner did nothing but lie to me and neglect the property the entire time I lived there. Just a few examples:

I was told the apartment would be cleaned and repainted before I moved in. This NEVER happened. I eventually purchased very tasteful light cream & sage paint & repainted the apartment myself. When I tried to collect my deposit he claimed in maliciously painted the apartment without his approval and kept my $850.00 even though he allowed other tenants to repaint their apartments and paid for their paint because his terrible maintenance crew never got any work done. 

The building was in disrepair and the hallways constantly smelled like sewage. I even had my mailwoman state on video that it was very difficult for her to fill our mailboxes because the stench was so strong and offensive. 

The elevator in the building would constantly break and trap tenants inside. This happened the entire time I lived in the building.

The maintenance crew robbed the tenants. I actually caught one of them on security camera stealing my package. I made the landlord pay me for the stolen merchandise. A few years later a friend of mine lived in another one of their properties once again "without their knowledge" the maintenance crew robbed several of the tenants stealing their electronics, jewelery & cash. When the tenant wanted to move out because she was afraid to stay there he sued her for $5000.00.

The sewer backed up into the apt building and was left to sit for over 24 hours. Eventually the other tenants contacted the health dept and the landlord was forced to clean up the mess. Here is a link to the article in the paper about it. http://goo.gl/tYG68

The co-owner and brother of the landlord threatened to shut down the elevator on me and force me to haul my "f***ing" s**t down the 5 flights of stairs when I was moving out because he didn’t want to wait for me to use the elevator. 

He would send letters & make phone calls in fake names such as David Brennan & Michael Scott to tenants. If you tried to contact the office to speak to such employees you could never speak to them because they were imaginary. 

The roof leaked horrendously into the back stairwell. The stair well was also filled with garbage and was extremly dangerous. I sent a letter to the caretakers that this needed to be resolved as it was very dangerous. Eventually the water got into the electrical system and the the fire alarm would not stop going off. The fire department shut the building down and the landlord had to pay for all tenants to live in a hotel for three days because the apt complex was unsafe for tenants to live in. This is all public record. I sent a 30 day notice letter to the 2 tenants he had managing the apt/collecting rent (because you could never get him to do anything) stating that I feel the apt is unsafe and I am moving out asap. At this point I had not resigned the lease after the first year I lived there. He turns around and sues me for $3000! The magistrate told him to settle it with us privately because it was so rediculous and we settled on paying the court costs + $100. 

5 years later an aquantaince tells me she is currently living in this landlords apt building. I share my horror stories with her and she eventually expereinces many of the same things I went through. She tries to get out of her lease and she was complaining about the problems she was having on her facebook page. I commented that "said rental management company is the worst!" A day later this insane former landlord send me an email through my business contact page that he is going to sue me for libel for making malicious, untrue claims about him and his business. He is obviously stalking his tenants Facebook pages. He says he has been monitoring my Facebook page since 2009 (untrue, not possible and CREEPY!) and that he will soon "eventually,probobly"sue me. 

What is your advice on how I handle this threat?