I am new too and have not really gotten comfortable with the idea of giving out my opinion on others relationships yet. I have been mostly focusing on my own so far. But reading this I really felt for you.
I am concerned over the fact that you broke up with him as a way to work it out instead of just working through it. You are wanting a separation period to work on things but that doesn't mean he sees it like that. He seems to do poly differently than you like Redpepper said. I am worried that you may have just given him the green light to let you go and continue with her. You may have inadvertently sealed your own fate with this guy.
I certainly hope I am wrong and the two of you can work it out and come to an understanding. You obviously care about him very much. But I have been down this road before and I can tell you the scenery was terrible. I wish you luck, and I hope you find some sort of peace with in yourself during all this time.