Something similar happened to me. RockBird and I had been in the process of deciding whether to break up or not for over a month. Then, when it seemed we were getting back together, we had a serious discussion about the future and he told me that even though he was okay with a limited form of poly now, that in the future he expected me to be completely mono with him, and (if it came to that) if I liked someone else, that person could never, ever be as important to me or as involved in my life as my relationship with him was. As a person who loves easily and whose ideal poly relationship is poly-fi with two husbands, I felt like it would take a huge toll on me to make sure that never happened. We decided that even though we love each other a lot, in the end our vision of the future was different and we decided that we should break up.
The difference is that now I'll be dating his best friend, who lives with him, and will continue to spend as much time in their house as I was before the breakup. We're on good terms. I actually wanted to pull away, thinking that it would be too painful to stay friends, but both he and his best friend convinced me that it was possible and they'd still be friends with me no matter what happened. It was rough at first, but after a lot of pushing and pulling we're just tired and want to settle down and be happy. We're not quite "just friends", we're kind of between friends and lovers, but we recognize that we're not going to be together in the long run. It hasn't been easy on either end, but he has a lot of willpower, and I refuse to lose him from my life. As long as he's happy and we continue to be positive influences in each other's lives, I think I'll be okay.
It's difficult when a relationship ends...when I feel sad I think to myself that it's not that I failed or that I didn't do a good enough job, it's that we were just not compatible. That we gave it all we could, that we're both great people who love each other, but in the end we just weren't what the other person needed and that the kindest thing to do was to allow the other person to be with someone who will be that for them.
Sometimes I still feel sad about it, because he's one of the greatest people I've ever met, and I don't think I'll ever find a better team than the one he made with his best friend. If it was up to me, I'd marry them both. But it's important to realize that different people want different things in life and even though I'd like to be everything to someone, that only goes as far as the other person will allow it. An ex of mine didn't want to be friends after we broke up, and I felt like he was making a mistake, but I had to come to terms with the fact that if someone doesn't want help, nor wants you around, there's nothing you can do. I just thought to myself that I did the best I could and that I had made him a better person. That no matter what happened in the end, that my presence had a positive impact on his life.
I hope that my experiences and my learning process were of some help to you... It sucks now, but it does get better. At least you have Wolf, who (I hope) will be there to support you and help you through these bad feelings.