Jack is almost always assured in social situations, eg he can dance and Ennis can't, he handles the LaShawn situation as well as anyone could ( given her nature!). I alwys see his walking to the bar first as his showing his self-assurance - he knows what to do, isn't worried by how to behave, whereas Ennis has little idea. It reflects Jack's greater experience - he's been away from home, travels the country later, settles down in Texas, while Ennis ends up where he began. Jack often leads him, but can never lead him far enough, literally or psychologically, to take him away from his Wyoming roots.