I'd just like to say that the OP was a beautiful bit of writing. We've all been there, bud, and not many of us have the answers. It could be that she's seen the error of her ways, realised what she's missing out on and desperately wants you back. Alternatively, she could just be on the rebound and looking for someone to keep her company, not caring that she's about to do your head in some more.
My advice is to let her know how you feel, and tell her that you're not interested in getting back with her unless she's serious. Alternatively, if you think you can handle it, lower your expectations about the relationship and see how it goes with her. Your third alternative is to try to forget her and move on. Your choice depends on what you think she's up to, and what you think is best for you. But make your choice and sick to it, don't just let this happen to you.
Personally I'd go for option three these days, but then I am a bitter old bastard with an expensive divorce and many wasted years of heartbreak behind me. You are young; you have time and emotions to burn. Fall back in love with this girl and let her hurt you all over again. Write some poetry about it. Your post was halfway there: Mike Skinner would have been proud of that.
Esteban de la Sexface's advice is also something you should consider, however. Magic username too. I salute him.
Finally, next time you ask us for advice, please include pictures.
