Fraggle I hope you can clear your head to have a full talk with your DH.
I've just read the start of your thread and then skimmed bits where the talk is about the whole lap dancing and sex worker debate.
My take is that your DH hasn't lied to you. He concealed a situation from you, believing that you would be upset and so the best he could do was to stay quiet about it after the fact. In that alone he did seem to be thinking of your best interests (other than not going I mean)
Having decided to do that, rightly or wrongly, he went on to confide in a friend who in turn disclosed it to his wife.
This remained a closed secret until the woman dropped it out to you...whether she thought you already knew or not is possibly another thing for you to think about.
You know your DH better than any of us. You also know yourself. What is it that you want? do you want him to have stood up to his boss on this night out and said No, he wouldn't be joining him at the club? do you want him to have gone to the club but not taken a private dance? or would you have been less upset if he'd gone through with it all but told you immediately afterwards?
Are you more upset about him having gone to the club/had the dance, or more upset about his friend and wife knowing and you being in the dark?
Once you're absolutely clear on exactly what's upset you and what you expect from your DH now, you can start sorting all of this out.
It's not the question, but for the record I'm anti porn, anti sex trade and so is my DH, which is fortunate for us as the most important thing is that you're both on the same page and abide by it. For my own part I would be more upset at not knowing while others did know, than with him having gone once and under the circumstances you describe.