you are right..it's not your fault
I too play the guilt game often (but not as much as I use too!)
I usually manage to put it to rest by acknowledging that it is a disease and feeling a comraderie with other parents of "sick" children
we do not "blame" parents if their child is ill with any other disease nor do we blame a parent if a child has a serious accident under their watch...life happens and we need to accept that
well, I find comfort in applying the same standards to addiction...an illness with serious complications that we neither planned nor encouraged
having said that, I continue to fight for remission (as most parents do...)