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.
Although I agree Amy clearly had a self destructive personality (and would possibly have ended up an addict regardless of whom she was with) I'm sure a craving for sugary foods is associated with being on heroin. So it's likely she was addicted to heroin at that point, rather than fizzy Haribo
I've never particularly liked Blake, probably because I really admired Amy and wanted to see her sort herself out and get clean. Blake always seemed to be an obstacle in relation to her sobriety (although she was probably an obstacle for him also.) It was a classic and tragic case of two addicts who can't live without each other, even though their relationship brings out the worst in both of them.
I still miss Amy though. Despite all her flaws, she always came across as a genuinely decent, talented young woman who had rather severe mental health issues (which is probably why she turned to drugs in the first place- to self medicate.) Being famous most likely made it worse, since I really don't believe she ever realised how truly talented she was. I think she was used by a lot of people to make money, and people just started to see her as a product rather than a person.
This video of her with a fan breaks my heart, because I think it perfectly demonstrates how fragile and lonely she was, and how a lot of people were just interested in her image rather than her: http://www.youtube.com/watch?v=nQ41IItQyos