I'd ask this over on the students and graduates side. It reads like a fact pattern. I don't really feel like putting alot of thought in to this right now because it's late, but it sounds like you both could tread onto the shaky ground of defamation. Of course, truth is always a defense to defamation, and accordingly the burden is on the defendant to prove truth. If you've engaged in revenge defamation, you could be subject to a counter-claim. If you've damaged him in his job, there may be a possibility of sizable cha-ching for him. My advice, move on. It's not worth the potential expense.