I truly believe him, when he says that she is not the reason why, so there must be something else. And that something else must be me - of course. Dear Hopeful, My heart goes out to you because this kind of unthinking break-up is the hardest to handle. Well of course not, it's him. And he could have done it because he wanted a different experience than the one he had with you.
Men lie to keep from hurting our feelings, but they only make it worse.
Since he left with no explanation, that leaves you blaming yourself, but you should blame him. He's the one who didn't appreciate you enough. It's okay to be angry with him for leaving in such an insensitive way. The best thing for you to do now is to go on with your life and stop trying to analyze what happened. You may never really know the truth.