10 years on

My son has now been an addict for 10 years he is now 30 years old with children. His partner was aware of his problem before we where and already had a child on the way, our 1st grandchild whom adore. He has over the years seeked help and has been on and off
programmes over the years. I thought when I heard he was using heroin my heart would break
He was brought up in a loving home, good background and was a happy child.
So what happened, wrong crowd? curiosty? Receipt of money from a claim where all factors that led him down this path.
I thought heroin was bad but there is treatment for this and legal drugs which help to control this addiction. Worse is the crack cocaine and it feels as if there is no end to this.
He has been clean in the past and relapsed has had a spell in prison and was adamanent that was the last time. He has since relapsed with cocaine again and dabbling with heroin to bring him down as the habit has got so bad.
He cries as he does not want this life, we have paid for drugs to stop him stealing and going back to prison. We are lost and so is he and his partner and children who adore him.
We have just told him no more cannot afford to keep doing this and we need some commitment from him. He has said he will stop and I hope and pray he does for his own health and wellbeing, let alone hours, but I know we will always be there no matter what happens