My Secret BDSM Fantasies in Our Relationship

I've been with my partner for three years now. We're both in our twenties and everything seems perfect, except for one thing that I'm so ashamed to even mention out loud. It started last month when a friend introduced me to some online bondage videos, and it just...clicked something inside of me. Suddenly, every time we were intimate, all I could think about was restraining my partner in different ways. We have an open relationship, but I've never brought this up before because honestly, the idea feels so wrong with everything else that's right between us. It's like there's a disconnect between what our bodies want and what our minds know we should feel comfortable with. My head is spinning just thinking about it. The other night, we were out drinking and I found myself drunk-confessing this to my partner for the first time ever, not the explicit fantasies of course, but just the thought that maybe I could try something new in our bedroom. They looked at me with a mix of surprise and...interest? Maybe it's all in my head. Last week, I finally worked up the courage to tie them up while we were fooling around. The look on their face was unreadable, somewhere between fear and excitement. In that moment, I had to stop myself from fully going through with what I wanted most because it didn't feel right at all. But now, every time my hands touch them in a way they can’t escape from, the fantasy bubbles up again. How do I reconcile this dark little corner of me with everything else we have? And how am I supposed to be honest and open with my partner if I don't even know myself?