Vespoli- I don't want to say, "I told you so," but I remember telling you the only way to salvage her dropping interest level was to dump her. Now, it's too late for that.
...ok fine: I told you so.
Your best bet is to cut all contact with her and just find some new girls to chill with. It is SO much easier to find a new girl than it is to "fix" a broken relationship. Ironically, the best way to "fix" a broken relationship is often to happily date other girls--do this and she'll question if she made the right decision.
You are young and, as a result, your view of the grand scheme of relationships is myopic. This relationship served a purpose is teaching you to avoid certain pitfalls. Now, you will not make the same mistakes next time.
It is CRUCIAL to have a few failed relationships early on; they will help destroy the ONEitis that was your downfall in this one. I got dumped by my first 3 girlfriends; now, at 29, I have much more success with women---mostly, because I know that I can replace them if need be. This is a lesson I would NOT have learned if I didn't experience the feeling of rejection by someone I believed was a "soulmate."
I knew from your initial post that you were going to pay lip service to the advice given in here and then fail to implement it in any sense of the word. That is the elephant in the room at Sosuave--the fact that most of our forum advice about relationship problems goes unheeded. Your story is not one-in-a-million; it's actually quite run of the mill.
The good news is that it's all part of the learning process. You now know what you SHOULD have done, because we broke it down for you. Now, you can go forward without having to blame your failure on evil women, or your looks or height, or your lack of money, etc.
You will meet many other girls. You will dump some, and get dumped by others. But, through it all, you will improve until you reach a point where there is no guesswork involved and YOU are in control. That's what we strive for.