My father killed someone in a car accident -- and I can't stop blaming myself for not having taken away his keys earlier

I am sure that you have been the best caregiver you can possibly be. Dealing with our elderly parents is one of, or the, most difficult thing we have to do in our lives. No one ever trained us for this, and we just go day to day doing whatever we can for them. In your situation, what happened happened, and it is certainly NOT your fault, and you need to rid yourself of needless guilt, in order to continue your own life in peace. If you need to, seek out counseling. I have found this to be extremely helpful in the most difficult times. Good luck to you, and give yourself a pat on the back for all the hours and devotion you have spent dealing with your father. Sometimes things just happen due to fate, so try to really give up all your negative feelings about this.