Wait, so he busted her trying to cheat because he was trying to cheat, and then you still hooked up with her after that?
And as she walked away (and out of his life forever) she flicked the butt of her cigarette in his direction, thus igniting the (previously gasoline soaked) papers he held in his lap.
I don't even understand how this is revenge. She surprise informed him she knew he was cheating. I don't get it.