How is this for flirting??
Back to your topic, Jakefan
your question was about Ennis following Jack
and about Jack being willing to take the lead.
I just studied the scene of Jack and Ennis walking on the sidewalk, and in answer to "and why would Jack let him walk behind him."
Actually if you watch carefully you will see that Jack stays on the inside (their left) of the sidewalk with enough room for Ennis to walk beside him.
Ennis stays on the right side of the sidewalk but a couple of steps behing Jack,
As they get to the overhanging roof in front of the bar, Ennis actually steps into the street - maybe to get a wider view of the unfamiliar territory coming up.
Ennis really presents himself as the subordinate person in that scene. (or maybe sizing up his new buddy - lol)