I saw this film again after 6-7 years later.
People talking about parallel with Alma Jr. marriage and her words " Yes he loves me", but don't forget Ennis met Jack AND married to Alma when he was 19.
Like Alma Jr. believes that Kurt and she is in love, probably 19 years old Ennis was sure that he was in love with Alma... Without knowing what the LOVE is.
I think Ennis loved Alma as same way as just another guy like Ennis loves a woman, but his desire to be with Jack was stronger. Maybe the desire was stronger because they were never able to share a life together. Ennis is very pure and genuine character, but I don't think he understood what was happening to him when he was 19. Or even he knew it, he couldn't admit he was in love with Jack because of his internal/external punishment and fear.
I also sensed that when Alma Jr. said "Yes, he loves me", he felt envy and sadness that he couldn't admit relationship with Jack like Alma Jr.
So maybe the line after "Jack, I swear..." is "I will be true to myself..." or "I will be with myself like you wanted to be...? "
As we all posted here there are 100s of ideas coming out, so the open ended "Jack, I swear..." was perfect line for the film. Ann Lee is one of truly genius director who hasn't lost his integrity and creativity even after he became Hollywood movie director. Not many director can work like him. And in person, he is such a down to earth, honest, sincere and wise human being.
Very interesting post.
Welcome to the forum, mtkny!