I found this online and found it just hit the spot with how I feel:
“Guilt is surely one of the most overriding feelings of grief we experience. We torture ourselves with what we could have done differently. We play the scenes of our lives over and over again, and struggle to recall whatever our last conversation was before the tragedy occurred- how causal or trite it may seem now- why couldn’t we have expressed our love, said a meaningful goodbye? We judge ourselves harshly, see our faults and magnify them- why weren’t we kinder, more generous with our time or attention, and on and on… We make endless lists of what we could have done but didn’t do. We beg for just a moment more to love, to change, to make it different, or even for history to rewrite itself, for us to be taken in that person’s place. But instead, we are left with the terrible realization that nothing we can do will change what happened and we must learn to live with it. Her at this point, we cannot- we don’t know how.”

Guilt will be a part of your grief, apart you must come to terms with. Guilt is often so intense, it will overwhelm you. It is a natural reaction to hold yourself accountable. But at some point, you will need to realize that guilt is a feeling, not a reality.
While it is extraordinarily difficult to break away from guilt, listening to what questions it raises will help you to sort your feelings from the truth.
One way to do this is to ask yourself these questions, either in your journal, where you have been writing your story, or even aloud to yourself. Attend to yourself self- accusations and acknowledge, “Yes, this is what I am feeling,” and then ask yourself, “But what is the reality?” Chances are, you already know the answers. You just need to listen to them too.
Try this exercise:
My guilt “feeling” is (complete the following statements):
I should/shouldn’t have…
If only I had…
Why did I…
Why didn’t I…
Why did I let_______ happen?
Now change it to this. The reality is:
I did what I thought was best.
I didn’t know.
I can’t change what happened.
I did the best I could.
From an excellent book which I recommend to many who have lost a loved one tragically:
“A Grief Like No Other, Surviving the Violent Death of Someone You Love”
by Kathleen O’Hara
Kathleen is a therapist and tragically lost her college-age son, Aaron, who was brutally murdered on Memorial Day 1999. In the aftermath of his death she developed the seven-stage journey thay is the heart of this book. This book offers concrete, practical and compassionate steps for those grieving. Highly recommend this book.