My backstabbing ex-friend has been sleeping with a married man and I want revenge?

Uh, okay, why exactly is it your business what she's doing? It's not your husband she's sleeping with. Be the bigger person here and keep out of her life. In time, if she's really so bad, she'll come to regret her decisions. If you mess with her you'll just be an idiot out to get her. If you leave her alone you'll be a good person she should have been nicer to.