I just have some doubts given his past history of oppositional, immature behavior.
Getting kicked out of the military isn't like getting fired from a job. A dishonorable, or even a general discharge follows you for life.
Life is what you make it. Son has a history of addiction, but many, many successful people do. Many people make terrible mistakes and recover from them.
The possibility of erring is not a reason not to try and to seek your destiny. His covenant with himself and G-d is more important to him than the possibility he will err. He sounds like a young man of integrity who made a serious deviation in life, but retraced his steps, and built character from what he had learned and experienced.
Lovemyson, you and your husband never, ever lost faith in G-d or in your son. This victory of integrity and purpose and commitment is yours to savor as well as son's.
There are no guarantees in life, for anybody. And as long as there is life and breath, there is coming back, there is recovery, there is return. (At least in my faith, there is the belief.) The belief in redemption. Over and over again. If necessary. One hopes that son's life will stay on a steady and upward curve but nobody's does. We can only hope for the kind of resiliency and recovery that he has manifested. If he backslides, there is no reason to believe he will not find these same resources.
I believe this. I am SO HAPPY for you. I am SO HAPPY for him. Although I wish he was not in the infantry.