Trixie,

Is it possible that your leaving might have negatively impacted him in some way? For example, might he have been called upon to pick up any of your old duties in your absence, or was he perhaps asked to reconstruct any programs or processes you previously managed? Besides jealousy, which is my first guess, I thought perhaps resentment. Your leaving left a void, he filled it, and then you came back and took a better position for which he was not considered, despite the fact he was doing your old job in your absence.

Just a thought.