It fits into the a AITA format, but imo this format is not suitable for what OP is going through.
It’s not an uncommon part of the grief process relating to a traumatic death that a person feels like they don’t deserve to feel better. OP is in a seriously dark place and seems to be asking if they deserve it. They are using this forum to try and figure out how to handle their grief and depression. That is not what this forum is intended for. This forum also isn’t equipped to deal with something like this.
OPs describe his life as “destroyed” and writes that he only wants to stop other from doing the same “unforgivable mistake” as him. The man is not okay. Him asking AITA is feeding into unhealthy cooping mechanism, and for his own sake he should not be here asking it but instead seeking real help.