For now, let's assume he's single. Another likely situation is that he has a girlfriend or is in the middle of a break up. The best thing for someone in that situation is an ego boost from someone who finds you appealing. You have to admit, it's always nice to know someone is attracted to you. If this is the case, even though the two of you hit it off, it doesn't mean he was going to drop his girlfriend for you.
Old ties are always stronger than new ones, even if there is pain with the old.
When this is the case, it's very difficult to stomach, but the reality isn't favorable for your side. Think about yourself for a minute. This happens to many people and it's one reason dating is difficult. Nothing is ever a sure thing until you've been dating for a while. This is another reason he may have not called you.