Caught in the Moment of Desire and Guilt

I'm an artist who's been in a long-term open relationship with my partner, Alex. We've had an understanding from the start that we can explore our desires outside of each other as long as it doesn't involve falling for someone else or hurting them emotionally. It's been mostly just small flirtations until recently when I started getting really intrigued by a fellow artist at the studio, let's call her Lily. She's creative, confident, and there’s something about us that just clicks. Last night, we met up after hours to talk more. The conversation was electric; our hands brushed occasionally during discussions of technique and inspiration. We were both open about how we felt towards each other, but neither of us pushed for anything physical, respecting the potential mess it could bring into my relationship with Alex. But then something happened. As we talked late into the night, I found myself sitting on her couch as she got closer to me. Our lips met, nothing hard or intense, just a gentle brushing that still left both of us breathless. It was clear there were feelings there, and it felt like an instant connection. However, once reality set back in and the passion faded from those first few kisses, I panicked. This wasn't about making a choice between Alex or Lily; this was about being honest with myself and respecting my boundaries as well as the respect for what Alex and I have built together over years. I pulled away quickly, feeling awful for not just leaving when the flirtation became more than that but also because I know this will cause friction in my current relationship no matter how understanding or open-minded Alex is about it all. So here's the question: was what I did wrong given the context? Should I have never let our connection escalate past talk and platonic affection, even for a fleeting moment? Or is it normal to sometimes feel drawn into something unexpected when you least expect it, as long as both parties understand that it doesn’t mean anything serious or ongoing beyond those moments?