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.

Maybe he missed you but is not able to handle you returning in a different role? If so, starting a new relationship, slowly, over time, may lead to a new friendship. Maybe better than before — but different and starting over from scratch.