Hi,
I think that this is the future Jack, and I think that he was somehow headed to have alcohol problems. (He told Julia in one episode that his dad taught him to drink. Also, in the pilot, he complains that his drinks are too weak.) Yep, Jack likes to drink. The drug problems developed, too. Why, we don't know for sure. I know that Jack knows that he should have never left the island and desperately wants to return at any cost. He is sick of all the lying.??? But, I do think the future was real there.