Thank you Ann, Anya, TJP and Angelscry.
Ann, I know it is the right decision. His story and promises have not changed in the last 3 years. With the clarity I got from here, it is clear that he has no intention of stopping his using. It is very hard, because my heart is sore. I cannot pay for his addiction again. Even more, I cannot let my 17-year old pay for his brother's choices again.
I place him quietly in God's loving arms and know that He will do what is best for my son.