This is a great topic.
The thing that came to my mind about Ennis flirting, was his line 'Hell, that's more words than I spoke in a year.'
He was engaged when he met Jack and Jack already knew that at this point. So Ennis was telling Jack 'I like talking to you so much. I've spoken more to you than I've done with other people, including Alma.' And the way he feels comfortable enough to share this with Jack, barring his soul like that. Painful as that revelation might have been (Ennis basically tells Jack about loneliness and not fitting in), it tells Jack a lot, I think.
And the way Ennis looks at Jack after he tells him this, he must have known what message he was sending.
God, I love both of them in that precious scene! *sigh*
I love that scene as well, hell I love the whole movie. I do think it is very revealing that Jack has so successfully managed in a relatively short period of time to draw Ennis out of himself.He is so relaxed in his company, he is actually stringing together whole sentences.From that first solitary word, "Ennis" when Jack says, your folks just stop at Ennis, to actually volunteering added information, what a journey.!!
I still think when Ennis says he hasn't had the opportunity to "sin" yet is flirting.From a man as closed in as Ennis, to have moved from only volunteering his first name, to telling Jack he hasn't yet sinned is a quantum leap.
I am not sure he realises the depth of his attraction, as he has no benchmark to compare it with.So I still think it is almost subconscious.I do believe though that Jack has made him "feel" the way no one else in his life ever has.
I think he has already fallen in love, and it maybe feels like a punch in the solar plexus to him.He knows that something within him has changed, almost like a seismic shift.Hence the pawing the white out of the moon.He just does not have the life experience to know what is happening.When I first really fell in love, I was in my thirties, and despite thinking I was in love before, and being more worldly than Ennis, it still struck like a thunderbolt.I could no more verbalise it than I could understand it.It just was.In fact it still is.