YTA.

Cheating is obviously asshole behaviour and absolutely gives you the right to terminate the relationship and affect all those kind of things. I'm even all for being honest about telling people that was the reason. Obviously she is an asshole for cheating, but that ship sailed when you ended the relationship. It's done.

I just don't believe you get to ruin a persons professional life because of something that happened in a personal relationsship. There wasn't anything illegal, she was just an asshole to you. I'd go along with reporting this if you where actually morally upset about this on a basis of work place ethics. You're not. You want revenge. You're not doing this because another person wasn't promoted because your ex was fucking the boss or some other injustice towards anyone. You want her to suffer, which I get. It would make you the asshole.

That being said, it took very little thought before I realized that I'm an asshole. Report the bitch and her scummy boss who knew exactly what was going on. Live with the "guilt", they knew what they where doing.