You are not responsible for your patient's healing or survival. This is the fine line a caregiver must walk, a line I stepped over several times. Without realizing what I was doing, I accepted the responsibility for my loved ones' recoveries. When they died, I failed. Then I accepted the guilt that felt appropriate.
Simple grief is hard enough to live with.
Guilt-ridden grief is an impossible burden. Treatment is the doctor's responsibility. Healing is ultimately the job of the patient. Being good to and for the patient is the best you can do. Don't try to do it alone.