A Mistake at Work

I'm a nurse in my 30s, and I've been with my partner for five years now. We're good together, stable, supportive, everything you'd want in a long-term relationship. But there's this one thing that happened recently, something that's eating away at me. It was late night at the hospital. My shift had just ended, but I decided to stay a bit longer to help with a particularly difficult patient. John (not his real name) was there, he's not my type at all, but he has this charisma about him when he needs something from you. He always seems to find a way into your heart. That night, he started flirting with me in ways I never expected. It made me feel... special? Important? It felt like an escape from reality, the normality of my relationship seemed pale in comparison. We both knew it was wrong, but something about him just pushed all my buttons. We ended up in a private room where we couldn't be seen or heard. I kissed him and he responded eagerly. What started as playful banter quickly turned into a heated encounter. It's not like anything happened, no clothes came off. But it was too close, way too close. We both pulled away after realizing what we were about to do. I'm so conflicted because nothing happened in the end, but the thoughts of wanting him have been swirling around my head ever since. I keep wondering if I should break things off with my partner or if this was just a momentary lapse of judgment. Do you think it's fair for me to stay with someone when my heart is already elsewhere? Am I being too harsh on myself, considering we didn't cross that line?