My first few viewings, I started tearing up when the music started at the end of the Lake scene as Ennis started crying. Then of course, when he found the shirts, and the ending.
But I was surprised to find that in later viewings, one of the most emotional moments for me was when Ennis fought the truck driver after running away from Alma at Thanksgiving. That last shot of him enduring the kicks of the trucker brought home to me all the pain that Ennis suffered on a daily basis because of his love, his fear, and his self-loathing, and my heart just went out to him.