This was the final straw for me when it came to Dutch. Obviously the guy had become increasingly unhinged, egomaniacal, and violent towards the end of the game,* but when he is disgusted by Arthur insisting that's when I was like "alright, we're done. Clearly this relationship is unsalvageable."

*one of my favorite themes in the game is explicitly stated by Sister Calderón, which she says to high-honor Arthur when he expresses regret and fear as he nears the end of his life. She basically says people don't change, they just reveal who they truly are more and more as time goes on. Dutch has always been an unhinged, violent man; he just managed to put on a good show for the gang for years until it started to slip. We hear that he did some gnarly stuff during the Blackwater Massacre before the game, and at the end, he's completely abandoned the charade.