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. Let someone step in and take over for a while. Find someone you can talk to, then go ahead and complain to him or her. Join a support group.