I am sorry that you are going through this. It sounds like she is indecisive about things and, forgive me for assuming this, but from the sounds of your entry ... she is using 'poly' to go out and have her cake and eat it, too.
If there was no indication of being polyamorous since you've known each other (possesiveness, being hurt when cheated on... loving more than one person at a time) I'd call red flag here. She has stated that her heart belongs to her ex boyfriend. How about you? What's she done to assure you of your feelings and her love for you? It doesn't sound like poly to me...
I would continue reading posts here and possibly talking to her more. Bottom line is, if you are not happy and your needs are not being met at some level, you are probably better off picking yourself up and moving on. Better two years than 20 years, right? I wish we could give you a huge collective hug here, for I think you really need support.
YOU have to do what makes you happy. Do not change for anyone but yourself.