It was Cortese's decision to go, he could have stayed, but didn't want the owners looking over his shoulder checking how he spends the club's money.
Why MP would leave under these circumstances is bizarre. Is he saying he'll only work for Cortese? He might wait a long time for his next job. He might end up as a bank clerk in some Swiss bank.
If this situation has been ongoing for 3 months, surely he has spoken to the owners? Unless Cortese has kept this to himself, then what sort of loyalty does that show from him to the manager?