I enjoyed your story, perhaps as much for its unconventional ending as for the story itself. I found myself liking Tam and Corus as well. A lot of it could be elaborated on at some future point, if you had the desire to do so. Some of the transitions were abrupt (but still logical) which I realize is because of time changes within the story. Still, I'd love to have known how Corus took Tam under his wing, what happened with the other dragon to make Tam lose his powers (although I agree with you, I'd leave it vague because the hook of the story is we never know for certain until the very end whether Tam is really a dragon or it was all in his head.) I was a bit saddened when Tam killed Corus, although again, it was right in character for Tam as a dragon. If you ever expanded it, you could possibly continue Tam's adventures, and maybe show how his stint as a human did manage to color his perceptions even in dragon form. Moral of story, etc. etc.
Read the story now
In any case, all in all it was a good read. Thank you!