Again, I'm very sorry. I know your heartache. A lot of us here do. There is so much support here and other places. Find people you can talk to. Someone who can listen and support.
I'm not really sure what step you should take. But at least back off and start getting "your" life in order. Find anything, and I mean anything, to help you slowly draw your attention away from it as best as possible. Yeah, that seems like it can't be done. But you must try to do something.
As you have witnessed, you cannot do anything to stop her right now. It's time to realize you have to pick up your pieces and start putting them back together. It's about you know. I hope you understand.
Fake it until it becomes real. Start going dim, then go black. Find happiness in something - anything. Start acting like you're getting through it just fine and getting on with your life.
Don't hate yourself for the mistakes you've made. Learn from them and use them as motivation to do something different. You have a life. And even though that life seems empty and broken now, it can be repaired.
You don't know what the future holds. No one does. But we can prepare for anything by becoming stronger and learning how to react positively to better ourselves.
My prayers are with you, buddy. Though I'm not too good at it apparently. I'll continue and throw a few up for you.
Keep journaling your thoughts and actions. It seems to help me and there are tons of people here to help.
Me:42 W:43 M:03/08/98 SD17, D13 Found out about affair:12/16/10 Found out again: 06/22/12 Split: 06/22/12