What's the point of prison? - From a prisoners partner

My partner; who has a drug problem; has been sent to prison.
The judge said he will get the required help. As soon as my partner arrived at HMP; he was offered drugs; took some and has started asking me for money.
Seriously; what is the point of him serving a prison sentence for a crime related to drugs when he is using drugs in prison? Is the Government and criminal justice system for real? 
I have told my OH (other half) that he will not be getting any visits from me and he knows I will stick to my word.
To be honest; I am tired of standing by someone who obviously doesn't want to change things around. How much pain can addicts/offenders put their families through? I am poorly; I feel ill and I have literally had it to my back teeth of being led a song and dance by someone who is supposed to love me. Rant over; thanks for listening. From a prisoners partner.