Has there been a discussion on the Alma/Ennis marriage scene yet?
If not, I propose some remarks:
The wedding ceremony follows immediately Ennis's collapse at the end of the first summer.
The words of the priest about sins and evil are a direct hint to that breakdown and to what Ennis and Jack did on BBMT or, at least, as Ennis himself views it: sinful.
Watch Ennis during the ceremony: he stands hopelessly beside himself, barely knowing what's going on. The priest has to remind him that he may kiss the bride ("or I'll do it"). It's a very tender, almost shy and very friendly kiss, but not a passionate one (unlike in the reunion scene with Jack).
Some scenes later, we see Alma & Ennis in the drive-in cinema, he seems to be completely absentminded again. Alma has to "remind" him that his arm is supposed to lay on our shoulder, but he is barely aware she's present.
In the scene when Ennis leaves, years later, for a fishing trip, Alma says bitterly "Didn't you forget something?", she means the fishing material but also a kiss for her. A kiss she won't get anymore. Unlike in the reunion scene, when Ennis is leaving for the first time after the night in the motel, and giving her a "guilty" goodbye kiss after which she bursts into tears.
In the parallel scene in Texas (Jack searching impatiently for his "goddamn" parka, as Lureen puts it), he still finds time for a quite superficial kiss, nothing special, but nevertheless.