Addicts and alcoholics can't and don't keep promises. After engaging in long term recovery and working the steps (if they can get past step four, and the majority don't), they separate into two groups of people relative to keeping promises and truth telling.
The first group is people who become very honest, sometimes painfully honest and direct. I love these people.
The second group are people who it turns out are in fact liars and unreliable. These people are just as unpleasant sober as they are under the influence.
Your dude is in one of these groups, but until he is engaged in a long-term recovery program and truly starts sober living, you'll never know which.
Cyranoak