Trying Something New with a Stranger

I've always been content with my marriage, but recently I found myself craving something different. It started when I saw an ad for an art studio where models pose for the artists who frequent it. The idea of capturing someone else's beauty and form struck me as both exhilarating and terrifying. What began as simply observing soon led to a deeper connection with one particular model, whom we'll call Alex. Alex was intriguing, his body seemed to be made entirely out of lines and curves that begged to be rendered on canvas. After our initial meetings, the line between artist and subject blurred, and I found myself wanting more than just his image. We started exchanging phone calls and messages, and eventually, we met in a hotel room one evening. I'm not sure why this happened or what it means for me and my marriage. Is it just about satisfying curiosity, or am I missing something with my spouse? Am I being unfair by keeping this secret from her when there's nothing to show but an unfulfilled desire? What should I do next, if anything?