...It Was Just Once...?

I'm in my 40s and have been married for over two decades now. We've been together through thick and thin, but lately, I've felt so disconnected from reality... or maybe just from him. Everything started when I met Sarah at one of those networking events. She's younger than me by a decade, beautiful in a way that I hadn't seen in such a long time. We talked briefly about business, exchanged some emails... But then it happened. A few weeks later, we decided to meet for coffee... and things just got out of hand. It wasn't something planned or premeditated; more like two adults succumbing to an urge that shouldn't have even existed anymore. Yet there we were... And now I can barely look at myself in the mirror. Every time I'm alone, these thoughts come rushing back... and I find myself asking if this was just a lapse of judgment or something deeper? Should I be worried about my marriage's future because of it? How many people have cheated once and never looked back? I love my husband deeply but am terrified he'll find out. Is what happened normal, or should I feel more ashamed than I already do...?