I would say you should have a plan for how you would like to respond to the different bad situations Accuray lays out. You might come up with one or two points you want to make sure to convey to H if he starts focusing only on your issues, for example. However, you won't be able to control this situation, or your H. Would you want to if you could?
My DB coach recommended to think of yourself in this stage as a negotiator. You are looking for common ground with your H that you can use to start having constructive conversations. This will require a LOT of self control and listening on your part. Maybe the MC appointment will not yield results. That would be okay. Not every negotiation yields an agreement. I would say your goal should be to make sure it doesn't add strain or new wounds to your R. If you make progress, there will be plenty of time later to open up more.
I haven't had a chance to try this, but you might look for a MC who practices Emotionally Focused Therapy, or a workshop on it. This might be a better fit to your H's personality (reading between the lines here) if he is an atheist.
H: 38 xW: 38 M: 16 T: 18 S: 9 BD: 2/2012 W moved out 4/2012 D: 11/2012