To me this scene is the "deepest" It goes deep into the heart of the veiwer, When Jack and Ennis were on Brokeback one thing Ennis seemed to love about Jack was his practical joking. Now don't get me wrong, but the irony of the whole thing! Wow...Who would"ve believed Jack Twist WOULD'NT be around at the end of the movie? He was so full of life. I think Ennis was in awe of this and loved Jack more for it , so for Jack ,the, teacher, the guider,the lover, the one who opened up a whole new world of possibilty for Ennis would be "first to go", and push him into "if only I.....scenerios. Him saying " I swear" means that he swears that Jack really got him this time.It's a sad thing but Jack did leave the shirts as a testament of his love. Only then did Ennis know how much.