Feeling alone and cheated - from anonymous

Hello. I don't know where to start. My partner is in prison and we have a young baby together. He is always ringing me and asking for money and I can't afford it. When I met him and started seeing him I didn't know he was taking drugs. He told me he had been in prison before but I have never been around anyone who has been on drugs so I didn't notice. He was always round at his mates though so now I look back, something was obviously amiss. I feel cheated and when he got arrested; and his brother turned up at our house (who I had never met before by the way) it was his brother who let slip and asked me if he had been taking drugs again. I was floored.
I love him but I can't cope with the constant phoning asking me for money and even some other guy rang me on his behalf once. 
I feel scared because of the news stories about drugs in prison and the amount of times he asks me for money is extreme so I have no doubt that he is taking something.
He is released in February 2018 and this is something I don't want around my son. I just don't know what to do. I feel alone and confused. 
Please keep me anonymous. Wishes, Partner of prisoner.