I was in a Master/slave relationship of 11 years, we were poly, and it was fantastic- but also hard work, and failed in the end due to jealousy on the part of a third- the woman he brought into the family and married. She was vanilla. She "accepted" that I was his slave, and that he had no intention of giving me up, despite marrying her, but she never truly accepted it, and was for the second half of that eleven years a constant wrench in the gears. She fought with me. She fought with him. She hurled insults, demanded preferential treatment, (I'm the Wife... you're just his slave- which could have been fine and kinda hot, if she'd been fetish- but she wasn't and it was just nasty and ugly.) In the end, he divorced her, and left me- though he and I remained close. And though he never admitted it, I suspect he couldn't deal with the guilt of how much damage bringing his wife into our family did to us. (There were other play-slaves that came and went, and they and I always got along just beautifully.)
Still- I am 100% poly now, and wary of others who claim to be, simply because it's all well and good to claim to be poly, but everyone experiences jealousy, even rational, truly poly-minded people. It's what you DO with that jealousy that matters. Do you acknowledge it and talk it out, face it, come to terms with it, or do you let it cause pettiness and anger, resentment and pain?
For me, happiness and fulfillment equal polyamory. I cannot hope to be EVERYTHING someone needs. I would rather be the best ME I can be, to fulfill what I can, rather than struggling to live up to an unreachable goal, and likewise, I don't think it's fair to demand that anyone I care about be MY everything.