*comes back from unexpected sabbatical*
Mumei, you seem to be in a similar situation to the one I've been in for the past year. I've had bondage fantasies since early childhood, since before I knew what sex was, and was in total denial about it even after I started masturbating in adolescence. It was only in the past two years (since my 17th birthday) that I've been able to admit to myself and a few friends that I have a fetish. One of my biggest projects after this voyage of self-acceptance has been a quest to discover WHY?!
I knew that a lot of people seem to develop fetishes due to sexual repression in childhood, but my parents weren't uptight at all, so it couldn't have been that. I also knew that a lot of people seem to develop an interest in BDSM after sexual abuse, but that's also impossible- I've never been abused. My search for a concrete reason has even branched into past lives, for lack of anywhere else to look.
But more and more, I'm realizing that there's no single concrete explanation for why I'm aroused by (and only by) bondage. I'm still interested in finding an explanation, but I'm not so worried about it anymore. I'm more open to the idea that there are multiple factors at work.
If you're just burning with curiosity about where your desires originated, you could consider seeing a therapist or councilor of some kind. There are some who specialize in sexual deviance. That would cost money, though.
One more comment: the BDSM community isn't in the business of excluding people. Nobody should tell you that you're not "into BDSM" simply because of something you haven't done or something you wouldn't enjoy or a fantasy you haven't had. Anyone with any interest in any aspect of BDSM can claim to be "into BDSM" without being hounded out of the forum.
*slinks back into the shadows*