Hi, I saw this post and immediately had to sign up to say one thing!
Myself has accidentally killed 2 people in my life. The first being my mother who, after many years of learning to accept and forgive myself, had died shortly after giving birth to me. Occasionally I still find the words, "If only I wasn't born she'd of made it" perch on my lips. The second a girl who had killed herself because... long story short, she put herself in the hospital feeling like I'd never notice her and when I finally was told she was in the hospital, I visited her, and afterwards she took her own life. I lived in a small community and almost everyone there put such hatred and blame on me for her actions. I never bullied her or did anything bad, I just never knew that she liked me and never even saw her in the town. Yet the whole town still blames me for her death.
But I found the strongest thing that you can do for yourself in order to start forgiving yourself and putting in the past is to imagine those people you had taken the life from telling you "I forgive you. I understand what happened and I know it was tragic, but I forgive you."
As well as understanding your actual role and being real with yourself with what you controlled and not with what was "supposed to" or "could have" been different.
Life could be and is supposed to be completely different, but we don't focus on that when we can. We tell ourselves, this is what I did, and this is why, and now I know what can be done differently and try to pull yourself into the now and not let yourself drift so strongly back into those intense past memories. It's hard. I know I still occasionally find myself at my mother's grave or in that hospital and have to struggle to pull myself back to now.
I understand my experiences are not as direct as yours, but if the guilt was the same, letting yourself forgive yourself is strong.
It's only been about 7 years since that girl, and I sometimes still tell myself if I just didn't visit her or if I had talked to her and been more social to being with, I could have stopped her. But you have to realize what you really did and what you can do for next time and imagine that person saying, I forgive you. It can help quite a bit.
I know this is a few years late, but I only just recently had gone to counseling and been diagnosed with PTSD and major depression, and knowing others have also gone through such traumatic experiences kind of helps with feeling less alone and reminding myself I'm not broken, just trying to keep on keeping on with a bit more weight than some others.