As far as advice .. I need to read up on you, I follow read alot .. sometimes as you can imagine it feels like the same story, different characters with a few different plot twists. I do think there is a difference when dealing with a true MLCr vs a WAS, but there are some tools across the board similarities that can be used and implemented regardless.
So one of those things that may help regardless would be how your H feels and how you address/don't address this. I think the only thing you can do is validate and you need to remove yourself as the reason. I know my W used me for everything that was wrong, much easier to do that than look at ones self ... I was guilty of this too. So its about removing pressure, own your stuff but let him have his... he is sharing how he feels with you, this is good, you gain information. You can use this .. the STFU tactic is deadly as you gain all sorts of knowledge.
For me it was like you put it. "I do not want a D, sorry you feel that way." Short and simple non threatening responses. Let him talk it out, do not put pressure on him, at some point he has to see you are going to be just dandy regardless.
