Wow. That sounds awful. I'm sorry.
It sounds like she has her own agenda and she doesn't seem to concerned with how you feel. I have only seen your side of things... maybe you could invite her to join the forum? Read up on what she's doing?
It sounds to me like you are more upset about dishonesty and betrayal than non-monogamy.
I have to say that the "sharing" lingo bugs me out a little bit- even when invoked by her- she isn't property. She's a person. That said, it sounds like things are moving at the speed of light, and it seems difficult for you.
The only thing that you can request is to be treated with respect, and you can define what that means to you. You have to decide what to do if that respect never materializes.
Hugs to ya.