Caught Off Guard in the Backseat

I never would have imagined this happening. You see, I've been married for twenty years now, and things between my wife and me are generally good, loving, stable, fulfilling. But we're not perfect, far from it. There's always room for change and growth, right? Well, a couple of months ago, I was at this dinner party with old college friends. It’s one of those get-togethers where everyone is drinking more than usual and the conversation gets personal fast. We were talking about sex in relationships, and someone mentioned how important it is to try new things from time to time. My wife hadn't been feeling very adventurous lately, but I’ve always liked pushing boundaries a bit, within reason of course. This idea just lingered in my head, growing with every sip. Later that night, we were leaving the party together and our friend Alex offered us a ride home. As soon as we got into his car, he casually said something about us being an interesting couple to watch. That comment set off some kind of crazy thought process in me, I started thinking about how it might be fun for both my wife and I if she was touched by someone else. She seemed shocked but curious too. Next thing I know, we’re whispering back and forth about what could happen on the ride home. I can’t believe it, here I am, in my 40s, about to let this guy touch my wife in a way that’s never happened before. My heart was pounding so hard; I felt like I was going to pass out. Eventually, we ended up pulling over and sitting together in the backseat of his car. Everything just felt incredibly surreal and wrong at the same time. My wife and Alex...touching each other while my husband instincts screamed that this wasn’t right. But there was something freeing about it too, like a guilty pleasure breaking through all my years of being 'good'. I finally stopped them, but I don’t know if I’m relieved or disappointed. It felt so real and exhilarating for just those few moments, even as we drove home separately later. So here’s the thing, I’ve never cheated on anyone in my life. But did what happened that night count? Am I the asshole for even letting it get to that point? Or is this something normal couples can explore together with other people? I’m really torn up about it and need some outside perspective, any advice?