Heroin is usually something you get hooked on straight away, rather than during a long period of time. Of course only he and Amy know the truth and one of them is dead.
I'm inclined to believe an actual ex-heroin addict's account of the events as he was there. And I'm sure not every addict has exactly the same experience. He also has no reason to lie.
I think Amy would have been an addict whoever she'd fallen in love with because her personality was just wired that way.
Remember when she had the sugar addiction and was always off to buy sweets? An addictive personality was the death of her, not Blake.
Agree with this, JK asked Blake if he thought she'd be an addict even if she never met him.