Tok, I know you've been dealing with this for a while now. And I know it's a difficult thing to go through, having gone through something similar myself years ago. Forgive me for the lengthy post in advance.
Change is the hardest thing to accept for most people. Especially when you are the one who stayed the same and are left to wonder what happened to your relationship. I'm not a religious person, but the serenity "prayer" sums it up the best really: "Please grant me the serenity to accept the things I cannot change, courage to change the things I can, and the wisdom to know the difference." You know that she is no longer treating you the way you wish to be treated; you know that the feeling you once felt when you were with her has now become confusion, sadness and resentment. You cannot change the way she is or the choices she makes. You can only choose how you react to them. You need to start focusing on you and not depend on her to bring you happiness or fulfillment.
As far as her continually coming back around to you, it screams insecurity to me. She's obviously making huge changes in her life, and that is an intimidating, uncertain time for anyone. It seems to me that she wants to move on and wants to do so by jumping in with both feet, but she keeps coming back to the one source of reassurance and comfort she always had: you. It's quite possible that since she has pushed everyone else away (and probably pissed a good deal of them off in doing so), and she knows you love her and will always open your arms to her, she will continue to feed on your willingness to bolster her up and make her feel better about herself. That sounds kind of sinister, and I don't want you to misunderstand that I am saying she's doing something intentionally malicious; that's not it at all. I'm just saying, especially at her age, it's a strong possibility that she is subconsciously using you to ease her anxieties over this transitional period. Allowing her to do so is not particularly healthy for you, as it means you're going to be holding on to a thread that is wearing painfully thin. Someday she's going to cut that tie, or it's going to snap. I know it's painful to hear but, she's made her choice... everything she's doing and her clear disregard for how it is affecting you speaks volumes. What you need to decide is how you wish to remember what you had: as something that caused you increasing sadness and disappointment until it finally died or turned into something ugly, or as something that was special and loving and ended on mature, regret-free terms.
I'll leave it at that, I've gone on too long I guess. Just don't allow yourself to be used and manipulated by the memory of what you once had. There's nothing wrong with loving her as long as you feel it, but she's moved on, and so must you. Take care of yourself, I wish you the best.
