Breathe!! I can see that you feel quite gutted about the recent developments at H's work with the OW being transferred to the office.
It's no use running around like Chicken Little acting like the sky is falling. Try to find a way to get yourself centered and grounded. Truthfully, the M is not blown apart by this new development. It is one of those bumps that you two need to figure out together to navigate together successfully as a team.
In previous posts, it has been pointed out and you've jotted down as well that blowing your gasket has not been helpful at all. What can you do to rein back that tendency? Let's take a look at this from H's perspective.
If I try to open up even a bit, the W is gonna scream at me like a shrew. Why bother?! It isn't worth the hassle so I'll stay quiet. Not out of secretiveness, but to protect myself from the verbal onslaught from W.
Gee whiz...that's not the way to go, right? You want to present yourself as the calm and serene person that can handle hearing some tough topics and being totally present to hear H's thoughts, perspectives, and feelings on this new development. Because of your blow-up, you've missed out on a golden opportunity to hear out H. How can you two build on emotional intimacy if you keep blowing up at H?
How you react to any event is how you manage your emotions. Self-mastery means being centered and taking charge of your reactions. It is within your total, complete control. You are not a victim of external circumstances. Remember that, sweetie.
MDU, you even wrote yourself a pep-talk prior to the talk:
*remain CALM, get off the phone at the first signs of feeling too much emotion or any anger. Say "I need to process things so would like a break, I'll let you know when I can talk again" *know getting off the phone is an option but try to muscle through and show him that you can handle this. I don't want to let her threaten me and get me upset. *thank him for being honest and forthcoming. *force myself to ask specifics - usually I get too anxious and avoid, I think I'd be better off knowing it all, whatever it is, rather than hiding from it. *resist badmouthing her. Just let him judge for himself what kind of person she is for continuing to pursue a married man with small kids (assuming that is what's happening). *know that whatever happens I can deal. I can get off the phone and calm down. I can go to work and talk with one of my colleagues who has been really helpful. I will have the kids tonight and can focus on doing fun things with them. I can get through this. *no matter what, as long as I remain CALM, I WIN!!!!
You broke pretty much every one of your "tenets" here. All because of your reactive tendencies.
Work on this issue and pattern with the IC. Another suggestion is to count 10 (or even up to 100) before responding to H.
I am going to break this post up so it is not a super loooong one like our dear friend, 25, here.