Anonymous wrote:It's her ex? Yeah. She's fucking him.
I agree with this. I would go a little further and say she knew you were getting ready to propose and she dynamited the relationship on purpose. I've experienced this kind of thing - someone pushes you into being the one to break up, often by being so crappy that you have no choice. Lots of people sabotage a relationship they can't quite bring themselves to end like an adult.
Others have said this too, but I'll just add: there is nothing but time that will let you heal. It hurts for a long time and you have to grieve both the loss of the person and the dreams of the future you had. I wouldn't recommend getting serious with someone new, but I would definitely recommend getting into something casual with someone new.