I'm sorry to hear about how you feel like the rug got pulled out from underneath you. I remember just how bumpy things were with Roger when he first started dating Taylor and the number of times that we both THOUGHT we were on the same page, only to find that we were not at all.
I'll second what others have said about both of you contributing to the blow-up. This feels like the epitome of miscommunication on both of your ends. I'll also agree with tenK's thoughts about how this problem may go much deeper than it initially seems - the resentment is palpable. Consider the importance of working towards a healthier relationship before jumping into dating others. I get that you've been yearning for this for a long while, but if you want this to work in the long term, it may require a stepping back for a while to fix the relationship you're already in. Just one person's perspective.
If you do return to the conversation about opening up, here's a checklist that others had recommended to me in the past. http://openingup.net/wp-content/uploads/2011/08/Open-Relationship-Checklist-OU.pdf. It might help you and him to sit down and talk about what you're looking for in a partner and what he is hearing you say and willing to agree to at this point.
It does feel like a BIG step to go from closed to fully open without any restrictions in a matter of days, and it's not okay for him to be verbally abusive. I hope you get through this without too much pain.
I'm disappointed, but not very surprised, to hear that your husband is not okay about you seeing other men. I detected that part of the problem just from reading your first post.
This in particular:
"I have tried over and over again to talk to him and help him to understand I am poly and I am not being true to myself pretending not to be. I have expressed this but each time he shuts me down saying he could never be okay with me being with other men ..."
Obviously he has not changed in that respect. Now whether he purposely wanted to deceive you and make you think he had changed, I don't know. I'd have to know the details of your conversation with him. I do think you would have needed to specifically, out loud, told him, "I want to be with other men, not just other women." I even think you would have needed to ask him to repeat that back to you and make sure he understood what you just said. And then I think you would have needed to ask, "So, are you okay with me being with other men?" and go no further with the discussion until he answered that question.
What you'd need to do now is probably more complicated than what you'd have needed to do before, now that things have blown up and he is on the warpath. If you want to stay with him and don't want to cheat, you will need to wait a long time before you can talk again with him about poly. To be honest, it sounds to me like your marriage is in trouble, never mind about poly. I suggest getting a marriage counselor if you possibly can.
I'm very sorry he did such a 180° turnaround compared to the impression he gave you earlier. And I'm sorry he's being so mean about it all. I don't know how to convince him to stop acting like that, but I hope he will stop acting like that.
