You essentially got someone fired for thought crime. While in this instance, that thought crime coincidentally had a real life corroboration, it was a just a lucky happenstance. You were not in the ethical right here!

It could have been that you reported to HR a romantic fling between two consenting adults, while they had no intention of their private lives spilling over into the public eye.

Disapprove of your actions, and further disapprove of your schadenfreude at someone's firing