I disagree with alot of the replies here.
My position is the same as yours, it's so similiar and i'm in the stage where we don't talk anymore so listen to my advice and hopefully you'll lose some of it and that it'll be a great help.
Lesson 1, never get pissed off. Trust me, you want this girl and you love her so when things happen you get really pissed off. That's fair play, i was the same. Even though my ex was in the wrong, getting pissed off makes it so much worse. Like she said she was looking for a sign that one time, and what did you do, you got pissed off. Fair enough, i would of been the same. But look at it, if you didn't get pissed off you would be in a better position.
I only read a little of this thread and saw that it was so similiar to my position that i just had to reply asap lol. Trust me, getting pissed off is the key factor that'll lose her. If you want her, sit down, relax and promise yourself that you wont get pissed off. I know she is engaged but in life, sometimes it's "do or die." I had my girlfriend there, i made the difficult stage, perhaps maybe a stage just ahead of where you are at now. She then wanted to be with her ex, when bad stuff happened i got pissed off and eventually i lost her. If i didn't get pissed off, she would of felt less for her ex in time and i would still be with her, i still love my ex and i know how it feels to be in your position.
It sounds like she is really confused, it doesn't make her a manipultive person as some say here, in her position she is torn and doesn't know what to do. My ex used to weight my relationship up constantly, so when your gf/ex gf does this you got to make sure you come up on top. Either this, or let her go and be happy for her. Do you love her enough to learn to be happy for her? It's really hard, and in the time period you are now, i wouldn't of been able to do it, but i came 20% of the time.
Hope that helps.