Hi Beck,
im in the same boat. 10 years happily married. 5 months ago I get the I think we should separate then divorce. We've put the house up for sale but we're still living together. See my thread for more info. 
I get the same calmness when we talk generally but as soon as it goes to how she's acting or how it's affecting our daughter she freaks out, full of anger. She is in denial about having D but she is seeing her GP and has been assessed by the CMHT. I believe the AD's she is on are too low a dose but I'm not a doctor. 
I have gone through the same stuff as you trying to get answers or even her friend to tell the doctor everything she is feeling. Everytime she has found out I get the same as you.
This whole thing is devastating my heart goes out to you. I feel your pain. 
Firephil