(spoilers)
Since the beginning of the game I was hoping and even half expecting Arthur to eventually steal the Blackwater money and just run off with Mary. That would be my best ending, no Tuberculosis, no revenge, no fucking Dutch and Micah. Just Mary and Arthur running away from it all like John and Abigail should have.
When she wrote the break up letter I was literally heart broken and realized that Arthur for sure would die in this gang.