I guess that's just where I have to trust the therapist, right?
the MC needs to earn your trust - be ready to trust him, but only if he's trustworthy.
One thing he can and should do is short-circuit the 'shit on nekorb' stuff. He needs to acknowledge it and accept it, but he needs to confront your H on things like 1) nekorb was in the same M, and she didn't cheat; 2) if your H had problems with the M, t was his responsibility to raise the issues so the 2 of you could resolve them; and 3) your H's anger is his problem, and he probably should seek IC if he needs help in dealing with it (and it sounds like he does).
If the MC doesn't call your H on his crap, if the MC doesn't give you a lot of protection, if the MC doesn't treat the A as a giant bear that needs at least to be tamed enough to get into a cage, don't give this MC your trust.
If the MC doesn't protect you, you need to protect yourself - repeating points 1-3 above in the session could be a good a start.
I can't help mentioning that if your H is using anger as a way to shift blame and avoid responsibility, he doesn't sound like a candidate for R at this point. I know you've got extra stress right now, but detaching from your H may be the best way you've got to reduce stress.