Do you find that what excites you changes according to your partner?

This sounds like a stupid question - of course it does. But I don't mean necessarily how your partner is in bed or what s/he does to you, I mean like does your fantasy life and sense of what's exciting to YOU change?

I was with one partner for a very long time, and while the content of our sex life was pretty varied, the theme was basically bondage. Since then I've had erotic interactions with two people, one of whom was definitely a "mind fuck" kind of person and one of whom is very physically controlling but has no interest in obedience or voluntary submissive gestures, and limited interest in bondage.

What's a little disturbing to me is how easily I can shift my own sense of what's erotic, to the extent that my own stories and fantasies change according to my partner's preference. It's almost like the other erotic experiences have been erased. I had thought that I pretty much knew what excited me, but now I wonder if ANY of this actually excites me in itself, or if my own sense of the erotic is just another variable in pleasing my partner.

I've made this sound very black and white, and of course it's not - all of this falls into a context of power exchange and submission, which is why I'm posting here, and of course I would not be turned on by, say, a bottle cap fetish no matter how much it pleased my partner, but within these general parameters, I am troubled by how malleable my preferences seem to be.

So here's what I'm afraid of, and I've been trying for a long time to figure out how to ask about it - If you really like to please another person, how can you tell what YOU want, and not what you want to want because it would please him? How can you tell what's pushing limits and expanding horizons, and what's a sick willingness to go along with anything?

I wish I could ask this more clearly. It has been bothering me ever since I found that the act of acquiescing in something that I had previously found unappealing was itself very exciting.