It doesn't sound to me that he was a bad employee; after all, you saw potential, trained and promoted him.
It sounds like your only gripe with him was that he gave short notice. If he's not salaried, one to two weeks notice is acceptable, though tough on you, for sure.
It's possible that he could have lost out on the new opportunity if he didn't agree to starting quickly. Too bad for you, but that's how it works out sometimes.
Would you be complaining so bitterly...