Apologies for the previous misunderstanding. Since you contacted him, then if he were going to need her agreement to date you he should, imo, have tempered his reaction to you a little. Been a little more cautious, a little less, "Yes, I want to date you" and more, "This is something worth considering, let's all talk about it."
I've been "vetoed", from your point of view, by everyone from new girlfriends to parents to church elders. And not even from a romantic relationship, but just a friendship. Yes, it sucks when someone doesn't care about you ENOUGH to choose you when they're being told, "I'm not comfortable with you dating her/being friends with her" or "She's not someone you should be dating/friends with" but that's life.
You got a few pages of sympathy, but now you seem determined to keep arguing your side until EVERYONE agrees with you. Not gonna happen. You didn't put this in the Blog section, so people are going to voice their opinions. You're not going to get a consensus that You Were Right and She Was Wrong. You suggested something. She declined. Good for you for doing some learning about yourself, but she's not obligated to agree to try anything. She doesn't NEED an excuse to say, "No thanks, not interested." Then it was up to him to decide if he wanted to date her or you, which he did. You say it was her choice, but it was his too. Funny how you keep being understanding of his choice but not so much of hers. Perhaps because his is less of a rejection of you personally? Let me ask you this: if you could do it over again, would you rather he just tell you that after thinking about he wasn't interested? Or would you rather know the truth about why he decided not to date you? That's one thing I've been wondering about the "complete honesty" of poly- does it help to know he wants to date you but won't because of her? Or is it easier to move on from him if you're under the impression that it was completely his choice and decision with no influence from her?
Anyway, back on the subject, neither of them sound ready for poly, so if they keep going with trying to have an open or poly relationship I really hope they work on their own shit, because to KEEP hurting people they try to have relationships with WOULD be irresponsible and cruel.