I think it depends on the person, but with my fww, the bar scene was often a prelude to a ONS or just bad behavior in general. We had an agreement for several years before d-day that neither of us would ever go to a bar without the other. I kept my end of the deal, but she slowly crept back into stopping regular with the "girls".
After d-day I made it easy on her and made it a deal-breaker. She complained a few times and I told her life is all about choices and she is just as free to make hers as I am to make mine.
Good luck. If he enjoys it so much, he shouldn't have a problem taking you along. And if he does take you along, you should enjoy it too.