It might very well have been the first time. Something that also strikes is me is that brief shot of Ennis and Jack in the tent on their last night together. Ennis has his arms around Jack that may be suggesting that the roles have switched or that Ennis is more comfortable with showing his feelings and his need for Jack. Maybe Ennis was becoming more open to things, but it was simply, as it turned out, too late.
I think you're right, Buffymon, to suggest that the image we are given of them where, in sleep, Ennis is holding Jack says that Ennis is now "more comfortable with showing his feelings and his need for Jack." It is an image, of course, that is echoed at the very end of the movie once Ennis has reversed the two shirts. Once more it is Ennis holding and protecting Jack but now, alas, it is not the sleeping Jack he can hold on to but only the memories of those happier times.