Wow...very heart-felt soul searching go on here. I think the greatest gift you can give yourself is recognizing your own faults, but also seeing your own beauty and the amazing qualities you brought to the relationship. Then you have to be able to see that in your ex-husband; recognize his faults and the reasons you fell in love with him. The end of a relationship is never black and white, there are always grey areas. I think the process of grieving the loss will also put things into a more realistic view.
As the posters said above: Forgiveness is a gift you give yourself.