Why Did I Do That?

I guess it's time to confess something that's been on my mind lately. In a relationship with someone who is otherwise amazing, supportive, kind, caring. But there was this one moment last month when everything changed. It started innocently enough, we were both at a tech conference and I ran into an old college friend. We chatted briefly but the look in his eyes said it all. The rest of the night seemed to float away as I found myself back at his place, drinking way too much wine. One thing led to another and before I knew it... well, you get the idea. It wasn't a big deal for long, just one moment that I'll probably never understand. I can't really explain why it happened, there was nothing in my relationship lacking or anything. Just this sudden urge, this curiosity maybe? My partner trusts me completely and I'm terrified they'll find out somehow. But the guilt keeps nagging at me, even though logically I know it's not a big deal. Sometimes I wonder if it means something deeper about us, but then again, who knows? It's just one of those weird things that happen in life I guess.