Most Helpful Guy
I don't want to add more injury to insult, and I really hope that I'm right on this one, but it appears to me that either you were the rebound girl, or a relationship of convenience. Either way it's clear that he has never gotten over his ex.
I am certain that in some way he was attracted to you, but never really intended on establishing a long term relationship with you simply for the fact that he never really got over his ex. The fact that he would constantly compare you to his ex was a good indication that he would rather be with her than you.
His novelty in you possibly because you were different than the girls he usually goes for. He may even have had the intention of trying to establish something long term and sincere with you, but his undying feelings for his ex was too strong and possibly distorted his intentions with you if they were true.
As far as him going to her graduation, as a promise or not, he should have either stated to her that he was in a new relationship and would be bringing you along or wouldn't be able to attend at all.
To me the writing is on the wall here. He bought a new wardrobe, started working out (even cancelled dates with you just to work out) is a clear indicator that he is actually seeking to rekindle the relationship with his ex if at all possible. If it turns out that he is indeed getting "closure" it will clearly be because she turned him down and he may return back to you as a fall back, especially since he will be disappointed and again rejected.
The question for you is, do you want to be there as a second option for him, or do you want to close this chapter and move forward in your life. It will hurt, but you will heal and you will be free to find a guy who will see everything he ever wanted in a girl in you.