You were clear with here from the outset of your relationship that you are poly-oriented and that you want a poly relationship. She said she would agree with that, but her actions since then do not agree with her words. Any time a person's word disagree with their actions, trust their ACTIONS.
Perhaps she experienced a sincere change of heart, perhaps she is a cowgirl. Either way, she has not moved toward the relationship you've consistently been saying you want.
IMO, it's time for you to insist that your needs are as important as hers. You've been very clear that you want a poly relationship. If she doesn't, the two of you are incompatible on this basic and vital point, and it's time for each of you to find partners who are better suited to you. Better to make the break now than to let even more time be wasted.
Good luck to you, whatever you decide to do.