In talking to your partner(s), start small. Where someone might be overwhelmed by,"I want you to tie me up, beat me, dominate me all night/all day/24/7," they might be open to, "What do you think about, next time I'm on top, spanking me a little bit?" If s/he says no, not as much of yourself is out there, feeling rejected, so it's a little safer, emotionally. It also lets them reply with, "No, but how about I blindfold you?" or with a, "Hell, yes! And could you (fill in the blank) to me, back?"
I'll also pass along a suggestion I got from Ozme, which is keeping a journal. In it, you can express all of your BDSM thoughts, write notes for yourself about books and other things you might read on the subject, write out your fantasies, etc. This lets you get your thoughts together for yourself and gives you a "cheat sheet" of sorts if your partner becomes/is open to discussions about the subject. And, since you are hesitant to talk about it, fearing rejection if I understood your post, this is a totally safe place to be as kinky as your imagination will let you--and you won't reject yourself. And, keep talking here. I haven't been on the site for long, but I have found the people here to be incredibly supportive. The worst they will do is express concern if they think you are putting yourself in danger, which is no bad thing. Safe, sane and consensual, and communication are the two things that are mentioned most.
Good luck.