I am so very very sorry for your loss. You have received such good advice and support. I'm very glad to hear people are looking out for you and your boys.
You cannot blame yourself for this but I know how hard it is not to. I think writing down the good memories with your boys is a wonderful idea. I volunteer at a grief camp for children every year and something we always do is write a letter to their loves ones to burn in a big bonfire. I know when my sister died my mother wrote letters to her for years. I also did that when a close friend committed suicide in hs.
I cannot fathom the pain that you are in. You are a fighter and survivor. You are an amazing man. Please do not forget this.
