(((Linda))) You must forgive yourself...you know that David would want that.
The first and most important thing for you to do is take better care of yourself...obviously others are depending on you for their own well being but you have to take care of you first!
The burden of guilt is crushing...even "self assigned" guilt.
You are obviously a loving, generous and giving person. I for one, would feel blessed to have you in my family. Please know that you are part of a larger family by sharing your grief here.