Is it polyamory?
Without the full consent of everybody involved, no. With negotiating that in advance--and having had discussions about the possibility of opening things up is *not* the same thing--she's just openly cheating on you.
What people do is a more accurate measure of what they actually think and feel than what they say. She may say she loves you and wants this all to work and what she's done indicates that she doesn't give a damn what you think, as you're not an important consideration.
Walk on. There are other ladies to get involved with who will actually respect you.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.