OMG, this thread may well kill me! Every one of the moments you've all mentioned cuts deep. Shieldmaid, that list of yours hits so many of the beautiful Jack moments, it's like reliving his life all over again. :'(
The compassion and pity I feel for Ennis can't be compared to the heartbreak that Jack generates in me. His openness makes you want so to protect him, always, but he puts himself in harms way from the moment he and Ennis are bonded together. Would probably tell you it was worth the cost, too.
My heart starts breaking for him the morning after FNIT, when he walks out to catch Ennis about to ride off .. there is a quality in his voice when he says "See ya for supper", that just screams vulnerability, I think. And that look on his face, like he's waiting for what's coming next and doesn't expect much good to be said to him, although the hope is so strong you can almost touch it.
IMO, there are few scenes where you don't see Jack's love for Ennis, and I say that about his trip to Mexico, too. A great love lays itself open to great hurt and can send you on paths that might never otherwise be travelled. So I guess I see a lot of Jack's love for Ennis not just in the sweet things he says or does, but also in those moments when he might appear tainted to some.
OT - Tpe, I think we are united in our admiration for Jake Gyllenhaal, for how surpassingly brilliant he was in the nuances of portraying Jack Twist. I only see Jack Twist, never Jake when I'm immersed in BBM.