Yep, I've noticed that too, he's definitely crying, and so am I usually :\'(
Something that got me about this scene the other night is that Ennis, for all his anger and hurt, is actually quite accepting of Jack's "infidelity". Whether you agree or not that Jack was wrong to sleep with other men (personally, I don't blame him, but that's just my opinion), most people in Ennis's place would've ended the relationship right there (and if, as has been suggested, Ennis was looking for a way out of it,this was the perfect excuse), but Ennis doesn't finish it, he doesn't even threaten to finish it if it happens again, he just tells Jack he never wants to know about it, so he's really giving Jack the go-ahead to carry on doing it, so long as he, Ennis, doesn't find out. Whether Jack would've carried on, and whether he would've told Ennis the truth if he asked him, is another matter, but it shows how much Jack meant to Ennis, that he could hurt him so badly, but he would rather turn a blind eye to it and forgive him, than be without him.