Being devil's advocate here, but - if things aren't said, then at least the door is left open. Ennis doesn't say, "Well, that's it," or the equivalent. He doesn't have the words to say, or even the ability to analyze internally, what he's feeling, even if he could bring himself to, and I don't know at this point whether Jack does either. In a sense they're both surprised by love, like people swept under by an enormous wave. Remember Bassanio in "Merchant of Venice"? When Portian says she is his he replies,
Madam, you have bereft me of all words;
Only my blood speaks to you in my veins,
and I think this often happens betweeen the two of them.