If you know what you want and you're willing to wait until it comes along, good on you. That's not so much idealism as having personal standards and needs in a relationship. The question then becomes "Can you handle being single until you find what you're looking for?", I suppose.
The thing about sudden revelations of polyamory is that they can result in what happened to you. Everyone's got the right, no matter hir relationship orientation, to decide hir own boundaries in this respect. It sounds like your ex had a hard limit when it came to monogamy. Consider the alternative for a moment. What would have happened if she'd gone along with poly, you'd got another SO, and then all of a sudden she demanded you choose?
Yeah, now three people are screwed! So you sort of dodged a bullet there, mate. She was honest with you (and honesty is one of THE building blocks of polyamory). She knew what she needed and that you could no longer provide it. In other words, she had her shit together, something GalaGirl would call "playing like a Jedi". (Yes, GG, I'm listening and learning!)
So welcome to the world of people who can openly and honestly be polyamorous with you, or know themselves well enough that they can be mono while you are poly.
The hurt will fade in time, though I don't imagine it'll ever completely go away. I still have angst pangs over a girlfriend who left me nine years ago. Oddly enough, I was displaying proto-poly desires. I wanted this one! No, I wanted that one! No, I wanted the one I had! Ohhh, frustration. For everyone. And my lady friend left. Don't blame her, am proud that she's gone on to Great Things, but damn, do I miss her.