He isn't so much defending as saying my rage at her detracts from my anger t him. He thinks that me going into rants about how much I hate her is my deflecting from how much I hate him. And it is to an extent. And I guess its also selfish of him as he finds discussion of her difficult as hes ashamed.
I think you're starting to get at it, with what you wrote above.
Try reversing the situation in your mind. In this scenario, you cheated on your H with his good friend. Now, post A, your husband is seething mad at his good friend and continues to be this way. Wouldn't you feel like, geez, if he's that mad at his friend and hates him that much, how much must he hate me? I'm the one that betrayed him the most. I was married to him! In this scenario, if your husband came to you and said, ok, I'm done with my x friend, it's you and I that now need to heal and grow,mean you see how that would make more sense, possibly?
I haven't experienced a double betrayal. I can't imagine how horrible that would feel. I'm sorry you're struggling with your feelings toward your x friend. But, I'm of the opinion that your H's betrayal is much, much worse. From what you wrote in your post, it seems like you might be minimizing your feelings toward your H and maximizing your feelings toward your x friend. If that's true, reversing your focus may help.
Best to you.