Take the part with what you have control over and put it aside. My wife has been gone for about 10 months now - she has done some callous things and made some mean, hurtful remarks. But I made the choice from the outset of our problems that I would not let anger take control of my actions. And I have done a fair job at it. The amazing thing is that once my wife realized that I truly was not going to sink to her level, she began rethinking her actions and words.
Anger breeds anger.
If you choose to stop the hostility starting with yourself, you will be amazed at how your stbx will react. It may not be immediate, but he will soon realize that you are now taking the higher road in all of this. Choose to focus on your love for him if that helps. Don't let the anger cover up your pain. I wish I could tell you that establishing a friendship like you discuss would be easy.