Yes, Jack is clearly implying that if Ennis was going to be there, he would, or could, be there too. As soon as Ennis mentions marrying Alma - why shoud that prevent his going back to work on the mountain if he hadn't found permanent employment? - Jack clearly reads that as saying that he wants to close off this chapter in his life.He does try, by saying that he'll be back if the army doesn't get him, to tell Ennis where he'll be next year. Ennis's response, "See you around" seems to me the equivalent of "We must do lunch sometime" or "I'll give you a call" ie a polite but meaningless form of words. This is why, IMO, Jack doesn't offer him a lift and drives off in tears.