Sorry to disillusion the last 2 posters, but there is no verbal communication of any sort in the scene from the time Ennis leaves the kitchen until he returns to the kitchen. The subtitled version of the movie shows every verbal exchange in quotes, and audible sound, such as horse neighs and bird caws, in parenthesis. Ennis is struck with emotion at finding these shirts, and as he gets his first whif of the shirt, he inhales (we hear it), then brings it closer and at the same time squeezes the sleeve with the blood. At that moment he takes 3 quick breaths, as one does in a mild sobbing attack, and as his emotion takes full control, his lip shows a slight quiver. These are normal, but uncontrolled facial movements of anyone in the early throes of expressing the emotion of grief.
I think a lot of you who believe you hear "I love you" do so because that't what you want to hear, and also because of the power of suggestion. Because this move uses a rural western dialect, with sobbing, chocking up, tears, etc., you fill in the blanks, so to speak. Unfortunately, there are no blanks here; no "I love you"...