It ocurred to me the other night that Ennis says "come here" to both Jack and Alma, just before the reunion kiss, and then when he kisses Alma goodbye the next morning. I'm not saying there's any significance in that, it's a normal thing to say, but the fact that he says the same words before each kiss just emphasises how differently he says it, and how different the kisses were.
I think thre's genuine affection there when Ennis kisses Alma, as well as guilt that he's betraying her, but there's no passion whatsoever (I agree with aintfoolin, I don't see any passion in any of their scenes together) unlike when he kisses Jack. Ennis knows that Alma can never come close to making him feel the way Jack does, but he knows that "ain't her fault", and I think he feels the need, as jacks_key says, to reassure her that he still loves her in his own way, and to reassure himself too, that he's still a regular straight guy with a wife and kids, even as he can't wait to get away with Jack.
