The reality is none of us knows the whole story. We are getting one side of it. It's entirely possible the problem is with the guy asking the question and alway

The reality is none of us knows the whole story. We are getting one side of it. It's entirely possible the problem is with the guy asking the question and always has been. Assuming good faith, honesty and a reasonable degree of accuracy on the part of the OP, looks to me like he should probably plan his exit. Not necessarily drop his resignation today, but start making plans. It's absolutely true that if he ups his game, he may find things improve and he can work with this person effectively. Or he may not.