OK... so one thing that helped me get through episodes like this is what I learned in my support group.
Sit down in prayer or meditation. With you I know it will probably be prayer, right?
Try to be still, with God. I always think, "Be still, and know that I am God." And it helps me to be still and wait to hear His voice.
I ask God to be with me, to guide me. And then I turn my attention to the grief/pain/despair/whatever it is I'm feeling. If I don't know what it is (and for me, it used to be mostly fear) I try to identify it. To look at it.
When I can see what it is (say, the loss of your marriage, when you expected to be married forever), I try to immerse myself in it. I think of it as a pool I just wade into.
I spent a lot of time in this pool, staring at the tableau of Mr. Gritty and OW at family gatherings, at work functions, at barbecues, etc. I think of him holding her hand, telling her he loves her, etc. I think of my kids going to their wedding. I explored every aspect of this pool, every crevice.
Somehow just looking at it this closely helped me through the worst times. Did it help me when I found a tube of her mascara in Mr. Gritty's bathroom? NO. It doesn't grief-proof you against future pain. It does, however get you through the bad episode of grief/anxiety/whatever, without avoiding it or evading it.
Now my pool is filled with other images. So will yours.
Another thing: your friends. You need somebody you can call who is a friend to your marriage as well as a friend to you. Somebody in the same gender who can listen to you sob without judging.
M:54, H:55 T:33, M:27 12/13 BD: EA 01/14 BD: PA, H leaves 03/14 H & OW break up 05/14 H says he will file for D 08/14 H initiates D 09/14 H wants to R 12/14 Still bungling our way through R