Hi mnmnl,
I pretty much going to repeat what others have said. Your brother's addiction is not your fault and it was not your responsibility to monitor his behavior.
My brother isn't an addict, but struggles with many other things in life. I spent almost my entire adult life feeling guilty about the life that he was living. I'm older than him and always felt that I should have been able to help him.
One day in my therapist's office, she locked eyes with me and said "Raising your brother was not your job. You were a child too, it was not your responsibility." I started to cry and felt the weight of years of guilt lift from my shoulders.
Hope you make yourself comfortable here and are able to read the many useful postings that have been accumulated over the years (especially the "stickies" at the top of the forums).
No matter how much we love the addicts in our life, whether they recover or not is their responsibility.
Take Care,
db