Can you try this? When he is calm some time, ask if you can have a chat. Sit next to him, not opposite. Try something like: "I love and respect you babe. I see that you are unhappy. As your wife and closest friend I of course want you to be happy and well. I heard you when you said things are basically over. I am now seeing that you've been unhappy for a while now. I'm sorry I couldn't see that before. That must have been really hard for you, maybe even lonely. I see your unhappiness now and I am ready to help. I am not sure how best to help you and I want to understand your point of view. I think we need to go back a few steps in order to develop an understanding of our problems...before we got to this point today. When you are comfortable (that need not be right now) I am ready to listen to how you've been feeling. Let's stay calm and respectful toward each other. Let's hear each other out."

Maybe try to avoid evaluating his behaviors as a "huge overreaction" etc. Even though that could be true from your perspective, from his perspective it possibly felt justified...the phrasing could be hurtful to him and possibly trigger more anger and stonewalling. Try coming from a non-judgmental place of listening and understanding if you can.