Oh man. I am going to try and be gentle here, but there is no getting around that this is a MAJOR transgression. At least it would be in my and Mr. intuition's marriage. Your wife is going to be hurt and ashamed, and you get to live with knowing you weren't there to protect her when she was vulnerable. This doesn't let her boss off at all; what an ass! Waiting until the woman was unconscious to take advantage of her... This is just one of the reasons that swinging and drinking don't mix. I agree with Mr. Spoomonkey; you're definitely going to feel the heat from this one. The worst part will be when/if she forgives you for it. That's when you'll realize that just because she forgives you, it doesn't make it go away, and you're still left feeling like s**t.
I don't have much advice to offer except to be truthful and just brace yourself to accept whatever punishment she deems suiting. Throw yourself on the mercy of the court. Perhaps I'm making a bigger deal of this than it actually is, but as I said, it would be a huge breach of trust in our own relationship. Sorry I didn't have better or kinder advice.
