My Secret Kink I've Hidden for Years

I’ve been married to Sarah for nearly 20 years now. We have a solid relationship, but there’s this one thing that keeps gnawing at me and won’t let go. It's a secret kink of mine that I've hidden from her since the day we met. When we first started dating, I wanted to know everything about each other, our dreams, our hopes, all those fluffy feelings people talk about. But there was this part of me that Sarah just wouldn't get, or so I thought at the time. You see, I have a fascination with submission and BDSM play that goes beyond the usual stuff like blindfolds or light bondage. Over the years, as our relationship matured into marriage, things started to become more routine. We stopped trying new things in bed, and while we were satisfied most of the time, something was missing for me. It wasn't until about two years ago that I finally tried a bit of role-playing with Sarah, just one night where she pretended to be my boss and had me fetching coffee and taking notes, all while dressed professionally. She enjoyed it too, but afterward, I could see hesitation in her eyes. That's when I realized if I were ever going to explore this side of myself more deeply, it would have to happen on the sly. So far, that means reading stories online about dominant women and submissive men while fantasizing about being with a different woman who commands me like an employee at work or even as part of some twisted family dynamic where she’s my older sister. These fantasies have become more vivid and frequent, and I feel like a hypocrite. I'm not sure what's right anymore. Am I cheating on Sarah by keeping this secret from her? Or am I just being true to myself in a way that won't hurt anyone else? I’ve been struggling with whether or not to come clean about these desires and fantasies, but fear of losing the marriage keeps me silent. Every time I think about bringing it up, my palms sweat and heart races as if I’m doing something terribly wrong. What should I do? Should I continue hiding who I really am behind closed bedroom doors?