I think Jack was protective of Ennis too. Until their final meeting, Jack never tells Ennis about Mexico though he's being going for years, nor does he tell him about his rancher "friend" down in Texas. He knows both those things would devastate Ennis and wants to protect him. I think the short leash comment refers to how Ennis gives just enough of himself, time, sex, affection to keep Jack hoping and coming back for more and Jack realizes it.
I'm reminded of a line in a song - "that's just the price you pay for the chains you refuse". Sometimes people refuse comittment or offers of love because they don't want to be tied down or are afraid, etc, thinking another option is preferable. And in the end, they still pay a price. Sometimes even a bigger price as in the case of Ennis. Every choice has consequences.
I think men express love in different ways so the small things they did for each other isn't unusual. I think it was consistent with their personalities, time period and financial situations. Men think practical things and actions are declarations of love. My husband interprets spending hours doing yardwork as a sign that he loves his family. His thinking is, if he didn't love us, he wouldn't find it important for us to live in an attractive house, nor spend the time doing the yardwork. Like once how I said, that's a pretty watch when reading a magazine and he asked to see and then remembered and bought it for me for Christmas. So while I might find an "I love You" a more direct way of communicating how he feels, I take the declarations wherever I can find them.