To address the original question, I have to say that at every viewing, I've been quite sure that "All them THINGS that I don't know" is a declaration of love. Since it's Ennis, that's about all we're going to get on the topic of love, but that was LOVE, way past simple anger and jealousy. He isn't able to say how he feels positively, so yeah, it's threatening, but notice that (in the film), Jack isn't particularly fearful - he goes right on tearing in to Ennis.
There's only one other place where Ennis reveals the depth of his love in words, and that's where I first start crying in the film, because it's crushingly sad, and yet the truth of his love comes right through (again, this the screenplay);
Jack: "for how long?"
Ennis: "long as we can ride it ... no reins on this one"
That is Ennis's promise of eternal love, expressed in the only way he knows how, AND with a nice touch: expressed in a rodeo metaphor that Jack would understand. One of the most beautiful lines in the movie, despite the denial of the "kid and calf" living together that came right before it. Basically, 'we can't be together, but we'll always stay together". :'( :'(
His outburst at the last fight they have is a mirror of this line. He gave his heart to Jack and he must know Jack's heart is his, no matter what else Jack has done or will do to stay sane when he's away from Ennis.
btb