I wrote this about a year ago in my journal and decided to post.  This is the thought process that helped me start to move forward and build my current life.  Hope it helps someone a little.

You have to let it go.  To live a meaningful, full life after terrible tragedy, you have to let go of old concepts, old ways, really your old self.  If you don't, you can't make any meaningful steps forward.  Let me explain.
I lost my husband, J.R., five years ago, unexpectedly to a massive heart attack at the age of forty one.  After I finally grasped the concept that he was actually gone, I got stuck on the it's not fair.  Fair has no role in our lives.  None of us has been dealt a fair hand, or an even chance.  Just didn't happen.  You need to let go of the concept of fair.  It doesn't exist in the real world, the world we live in.  It is a construct we sell ourselves to pretend we will be safe if we do the right things and behave a certain way.  Everyone here lost someone way too soon, to some unfair unjust incident, disease or event.  And it happens every day.  Not only the evil are punished, sometimes the good are just rolled over, for no reason that we can comprehend.  Let go of fair, it does not help.  Once you let go of fair, you can accept what is and start building your life on that instead of wondering why it happened.
The why is the next thing you need to let go of, along with the what else could I have done.  It is all second guessing.  You will never really know the why.  You can know all the facts, statistics and details, but you will never know why the heart failed, why the cancer struck, why the car hit... These are all unfathomable mysteries that we will never understand.   And you could have done nothing more, or differently, you could not have been wiser, smarter, faster, loved more or better.  If love was the only criteria those we lost would still be here.  The why will keep you in one spot turning in circles, like a dog chasing it's tail.  Eventually, you have to let go of the why.
I know this sounds negative, but it's not.  Once you let go, you set yourself free.  You then can focus on the love you had and shared, the joy you had in your life.  The love becomes stronger, the pain loses some of its constant ache.  And you can acknowledge that you played a part in that love, and that joy, that you were worth loving and that you are still worth loving.  And you start loving yourself again and you start to build a new life one baby step at a time.  We all go through the why, the if only, the questions and the doubts.  But eventually for yourself, please give yourself a break, a breath and just let it go.
Hugs,
Val