My ex was an ex heroin addict. As far as I can tell, he has not used heroin since, but in the last 18 years (I still see him because we have a child together) he's had problems with: crack cocaine, alcohol, prescription drugs, cannabis, legal highs. He's been homeless and sofa surfing. He's lost numerous jobs. He pays virtually no maintenance for his child (although he does see her every 2 weeks), he's had a further relationship with another child born who he Also can't support, (which ended in a DV charge which I don't 100% know if thats true or not) , he's been arrested, he's been 'missing' , he's had long periods of unemployment, he's lost countless jobs. He's in debt up to his eyeballs with payday loans, overdrafts, bank charges, and is being encouraged to declare bankruptcy. He's now 47, unemployed and virtually unemployable, and has zero savings, pension, assets. The only thing positive is that he's never been to jail.
He is still one of my good friends because deep down he is a kind and affable character, and he has a good relationship with our dd, but I will say this: people don't usually become addicts when they have nice settled calm lives. The addiction is usually a manifestation of a whole world of pain and 'being clean for a year' does not mean in any way that this person is no longer 'an addict'.
I would think very carefully about beginning a relationship with this person OP. The truth is, if you explain your reasons, if he's genuinely clean and sorted he will understand your reasons entirely. He wouldn't want a relationship with him either. If he gets angry, Blames you, pressures you, guilt trips you- well that's all you need to know.
Good luck 