Blake, 26 - whose divorce from the 'Rehab' singer was finalised in August 2009 - insists drugs became readily available to both him and Amy, 26, when she became successful, and they indulged.
Speaking to new! magazine, Blake said: "It started after a few years. At first, we both enjoyed having a good time, but there were no drugs.
"But as soon as Amy started getting recognised, more drugs started coming into the equation. That, coupled with the massive fame she experienced, perhaps made her indulge in certain choices that I made that she wouldn't have in the past."
Blake is full of praise for Amy for overcoming her addictions but believes there were many people who would have been happier if she had stayed on drugs.
He said: "People have got to remember that she's come out of it and turned her life around when there were probably 20 or 30 people around her at some stage that would have had every interest in keeping her on drugs and made a lot of money out of her. Like me, she's managed to come out the other side."
Blake does admit that he and Amy were a bad influence on each other, and their relationship - which on occasions turned violent - was ultimately destructive.
He said: "At the time, we were so scared of being separated from each other that we didn't trust other people's motives. You just end up imploding and drugs took that pain away.
"We did try and make wholehearted attempts to stop on a few occasions and went to rehab clinics, but it just wasn't working.
Speaking about the physical and emotional pain of drug addiction, Blake added: "You wake up and you're poorly. Then you have to see somebody you don't really like to pick up drugs, pay a massive amount of money and then perhaps you can function throughout the day. The nature of addiction is that you have to persevere in it, otherwise the physical sickness you get is unbearable."