I was married to someone who was addicted to Crack. I did everything I could to support him and to get him to change. He made all kinds of promises. Finally, I had to walk away. He disappeared for a while, I assisted his parents by paying his pass due rent and moving all of his things into storage - I think I paid the first 3-6 months of the storage and informed his parents that if he didn't show up by then they would have to decide what they wanted to do with his belongs.
I remember, I had a breakdown the day I packed and move his belongings. Had it not been for a few of my wonderful, beautiful friends I would not have made it through that day.
Interesting, his mom blamed me for his addiction. I guess she had to blame someone. Little did she know (neither did I) he had been doing this since college at Cal Berkeley. One of his professors introduced him to the drug. Imagine that.
After about a year or so his mom got in touch with me and she apologized. I really didn't have to do what I did to assist and I hadn't even seen drugs before (up close and personal) let alone used them. I wasn't upset or angry with her - I understood her pain, it was my pain too.
Anyway, he finally got himself together and I believe he is still doing well. So it is possible for a flower to grow out of the concrete. It has been proven time and time again. Don't loose faith. Know that you have done all you could do up to this point. It is now up to him.
Said all that to say, sometimes even though it is hard, you have to walk away and allow them to figure it out on their own. I did everything from intervention to acting as a watch dog. However, when my ex-husband made his life change it was because he wanted to. Not because I forced him to. I had nothing to do with it.
Please, don't be hard on yourself. I know, easier said than done. I'll be praying for you and your son. Stay strong.