He told himself that he didn't have a fair reason to be angry with her for buying his lie so easily. His celibacy, his commitment as a whole, was as much a surprise to him as anyone. He'd set a precedent, one he'd hoped would be the start of something great. How could she have known he'd do something so unfounded if he couldn't predict its occurrence either? He'd given her no prior reason to believe he was capable of commitment, but rather so many reasons to prove he wasn't.
But, unfortunately, just because his mind could rationalize away her acceptance of his falsity, his heart wasn't automatically going to go along with it.
No, he was pretty sure his heart was broken. For the first time in his life, he knew what it felt like to be dumped, to be truly and thoroughly exploited and discarded like trash. He'd given unconditionally and had been met with less in return. It was a disheartening realization that he was to take away from the experience: the knowledge that he was vulnerable. He might be ostensibly invincible in some areas of his life, but in relation to her?
Weak. Defenseless. A failure.
It's called a break-up not only because the relationship is broken, but because... in the end… you are.