I just did, just a few months ago... the same thing. I had to forgive myself for leaving my M and hurting my kids.... when I KNEW, KNEW in my heart, it was the decision I had to make.
That may sound like a real cop out to a lot of people, and maybe it is... I wont' rehash how I came to my decision or why, for it doesn't matter to anyone else.
I did the same thing for my abuse... for I forgave my abuser many, many, many years before I ever forgave myself. And not until I forgave myself, could I actually heal.
It's one thing to say it, it is another thing to actually DO it. To no longer carry the shame.
There is a saying about Justice. Justice is paying for a crime once. Suffering is paying for a crime, over and over and over again. Shame IS suffering, and it is completely and utterly ego based, believe it or not. For in feeling shame, you get to always keep the attention on you. "My God! Look what I did! Look what I endure! Etc., Etc."
If you forgive yourself, there is no one left to blame... and you have to move on and.... live.