Let me first say that I have read some of your other posts, and you are certainly worthy of your kids!! I think you are a fantastic mother. And none of this is your fault!! You wouldn't blame yourself if your husband got cancer, would you? Addiction is a disease as well, one that has the power to destroy lives if left untreated.
It will take time to let go of past dreams, but when you do you will be able to move on to bigger and better. There is definitely more out there for you, for your kids. Have you read the sticky called "the brain chemistry of being a loved one"? I read that when I'm feeling sad, and it helps put things into perspective.