I'm deeply sorry for your loss and crying my eyes out reading this thread. I too lost a bird to a horrible accident and even though it was 2 years ago the pain is still pretty fresh.
Saffron was a dark-eyed yellow clearwing budgie that spoke a few words and phrases and absolutely adored me. She used to fly to my shoulder all the time to croon a few choice words in my ear. Something like "Crikey, love you pickle ******* hello Saffron" was her usual phraseology. She used to stand on my collar with her head behind my ear and one foot twined in my hair.
One day I thought that was what she was doing and sat down in my wheelchair. It turned out she was hanging upside down from my collar and her neck was broken against the handle of the chair as I sat.
I've finally forgiven myself for the accident itself but I don't think I'll ever stop missing my small sweet yellow Peep of a budgie. Don't beat yourself up for your own mistake, try to focus on the bond you and NumNum shared rather than the cause of death. He was happy and adored and you gave him a very good life.
The Zombie Mama is here!