...Was I the Asshole?...

So, uh... I've been wanting to confess this for a while now. It's about my best friend Alex who's also in her twenties and is bi... yeah, that part’s important later. We grew up together since we were kids and she became like a sister to me over the years. Last month when visiting home town with my wife [let's call her Jamie], I noticed these intense feelings for Alex again. It wasn't just friendship but something more carnal too, if that makes sense? Jamie’s away on business this week... so after we talked and made sure she wouldn’t be back before Sunday night at least... Alex and I decided to go ahead with it. Both of us adults here, fully consenting to what was about to happen. I arrived at her place Thursday night and there was a nervousness in the air that quickly turned into an animal lust between us. She kissed me deeply as we undressed each other, my hands exploring every inch of her soft skin... Soon we were lying on her bed, naked flesh pressed against bare skin... I could feel Alex's body shaking from arousal, a slick wetness coating my fingers as I explored her most intimate parts. ... The next morning, it was like no time had passed at all between us. We showered together, washing each other’s bodies thoroughly, the sensations just as strong and electrifying as before. ...But now that we're back to being friends again, I keep wondering if this is normal? Or maybe a sign of some deeper issue in my marriage that needs addressing? ... Anyone else ever been in a situation like this? Is it just me or did this whole thing cross lines and make me an asshole? Am I being too harsh on myself or should I be more concerned about the implications here? ...