You didn't fail your son, I haven't failed my son...we loved them and as mothers felt that it was our job to protect them. Our sons both knew how much we loved them. But the sad truth is that addiction is stronger than a mother's love. If it wasn't, not one mama would be here posting our stories.
Before we moved a few years back, I worked for 2 years at a rehab, and like you, it was so very rewarding to be able to give something back to a place that gave so much to my son. I too knew that not all the residents would get clean and stay clean, and my heart broke every time one of them went out and died. But I knew I was doing "something", something to help maybe one boy, maybe one mama who talked to me, and maybe the world was just a teeny bit better because I was there.
No dear SG, you didn't fail, I didn't fail, even our sons didn't fail. We just each lost a hard fought battle with addiction. We tried, they tried, and we all fought hard. But sometimes the good guys don't win the battle...but that never ever makes them losers...because they fought as hard as they could.
Hugs from this mama's heart to yours.