Hi,
sorry for your loss of Zachery and the ongoing addiction that Andrew is coping with. I hope you are seeking help for yourself. A grief support group and alanon is a good place to start if you can not afford counciling. They are easy to find.
If Zachery's attitude was the same as Andrews attitude that treatment is for pu**ys I'm not sure how the system would have helped Zachery or how the police was supposed to find Zachery when even he did not know where he was at.
I can attest that less than 1/10th of addicts get and stay clean after their first treatment. It's not a cure and if there is no support or effort on the addicts behalf there is almost zero chance they stay clean. That's just the cold hard facts.
You are astute is worrying that you may lose another child.
Grieve Zachery but focus your efforts on helping Andrew. There are Narcotics Anonymous meeting all over the world. If he has the will to follow the program he can find a better way to live.