At the end of the film, when Victor and Thomas returned to their reservation, Thomas asked Victor if he knew why his father left, his response was that he didn't he meant A. I don't think Arnold ever intended to leave even though he talked excessively about disappearing, he loved everyone too much. When Arnold left, I think the regret of leaving him ate him alive, which is why I consider it the fourth heartbreak. Remorse and constant wondering what life would have been like if he hadn't left tormented his heart and mind every day he was away. I believe Arnold living with this remorse caused his to break down