My Kink No One Understands

So I've been with Alex for almost three years now. We got together when we were both twenty-four and it's been good overall, you know? But there’s this one thing that gets me in the headspace, bondage. Like actual rope stuff. Not just the handcuffs or blindfolds kind of thing, but real rope play with jute twine and all. Alex doesn't share my interest though. I've tried to introduce it as a game, you know? Just something different we could do together for fun. But every time they back away and say no thanks. It's not like Alex doesn’t want to be sexual with me, that part is definitely there and strong. We just don't click on this one thing. Anyway, I was hanging out at a friend’s place the other day. This friend knows about my thing for rope play but they have zero problem with it. One night, we were watching some movies and things got heated between us. I couldn't help myself, my hands started to move towards the jute twine stashed under their bed. I wanted more than just touching, something deeper. I knew it was wrong to do this behind Alex's back but... well, let's face it. Sometimes I need that kind of touch and feel to get off. So there we were, in my friend’s room, me wrapped up in twine like a gift. They were into it too, which made the whole thing even more confusing for me. It felt so good but also wrong at the same time. I guess what I'm asking is, am I being unfair to Alex by exploring this with someone else? Or am I okay to keep on living my truth and having that part of my life separate from our relationship? It's a mess, isn't it?