Living in the past, living with the past, and cherishing the past are three distinct things. Some people can't tell the difference and misunderstand moving on as being ungrateful. If he let his decision lead him to this state and wait for others to fix the problems that decision creates, then that's his choice, and let it be. Everyone has their own trauma, so don't let their trauma affect you. Remember, your mental peace, joy and happiness are what truly matter.