Am I enabling my son in prison? From YD

Hello Prison Widow.
In many many ways I agree with you about prison visiting and the drug addiction problems. 
My son is a drug addict and he is in prison. This is his 2nd prison sentence and I am visiting all over again. 
I thought that I'd done with it and that his 1st sentence would be the last. 
Maybe I went about it all the wrong way because he wanted for nothing when he was in prison the 1st time around because I rallied around and made sure he had everything he needed. I'm his Mum and that's what Mum's do but was I enabling him rather than helping him? If he asked for money I sent it; if he needed clothing and footwear I bought it and he always had phone credit to ring me every single night. But when he was released from prison; he was still addicted to drugs and we had a little family party when he came home in which he disappeared for 90 minutes and came back high. I knew because I was used to the symptoms and my heart sank. I didn't throw him on the streets but the cycle began again and he started pinching and borrowing money left right and centre. A long story short; I ended up being very ill and ended up on anxiety medication. 
He left and went living with other drug addicts who eventually got busted as they were caught dealing. 
He was sent to prison and I feel like I can't take anymore. He's phoning for money all the time and expects me to rally around like the first time.
When will this stop because it is killing me and tearing me apart.