"If the job had been a energizing one rather than one that had been so draining, this probably wouldn't have been an issue I resigned over." From this sentence

"If the job had been a energizing one rather than one that had been so draining, this probably wouldn't have been an issue I resigned over." From this sentence itself, it is a clear sign that he has reached "I am burned out" staged. Time to move on when that stage is reached.