It's completely understandable that you'd want to confront your wife for cheating, but I'm going to encourage you to be practical here. You have the ability to set the tone. If you weren't really bothered by it, or if the turn-on majorly outweighed your bother, it may not be useful to stage a full-on confrontation. A more effective route could be for you to just say that you know what's up-you saw it with your own eyes-and it really turned you on.
Your sign-off exposes the futility of your question-you can't uncreate a monster (I'm not calling your wife a monster; you did). This is a real be-careful-what-you-wish-for moment, but then I have to wonder what you were actually wishing for. By one measure, your foray into sex-club frequenting has been a smashing success. Your wife took to it like a horny fish to ... a bunch of other horny fish.