#1 Question About Betrayal: "Will the pain ever end?"

The short answer is "yes". When it will end depends on a lot of things: your personality, the depth of the betrayal (or your perception of the depth of betrayal), your support system, your spouse's behaviour, the affair partner's willingness or reluctance to exit your life...
In the meantime, there are things you can do. You might feel paralyzed, but by taking some control you'll be amazed at how empowered you'll feel.

Meet with a lawyer:
Having a consultation will help you figure out what your options are and what a separation/divorce will mean for you in terms of finances, child support and so on. Knowledge is power.

Just be:
Yes, it sounds flakey. But so often in our misery, we cut out the things that would actually help us feel a bit better. I spent so much time in my head (what's he doing right now? Is he still seeing her? Should I check his cell phone bills? Omigod I'm going to vomit...) that I forgot to just be in the moment. Sorry for going all Eckhart Tolle on you, but if there's anything betrayal can teach you, it's that you're not as in control of your life as you might think. This moment...and your response to it...is all any of us have. So try to just be. I finally got it one day when I was walking my dogs, something I loved to do...but had stopped doing because I couldn't obsess over phone records and Visa statements if I was out of the house. So...there I was walking the dogs, noticing that it was actually a gorgeous winter day. Blue sky, white snow twinkling in the light, the crunch of snow under my feet... And, briefly, I felt the weight lift from my shoulders. I lasted only seconds...but it was enough to convince me that it was possible.
What can you do to help you lose yourself...in a good way. Exercise? Listen to music (no cheatin' songs, please, unless they've about kicking a cheater's butt!)? Read a good book? Clean? (No kidding, a friend of mine gets great pleasure out of cleaning her house. Weird, I know!)

If all else fails...medicate:
Let me start by stating I have a strong but entirely understandable aversion to anti-depressants, as my mother had a serious prescription drug addiction for much of my life. I fought the idea of taking ADs hard...and kept fighting for 1 1/2 years after D-Day #1. But though I had moments of light (see dog-walking, above), rather than growing more frequent, they were growing less. And when I found myself more often than not wishing I could just die, it seemed prudent to at least entertain the notion of chemical intervention.
I was furious. I hated that everyone – most notably my therapist who's an MD – thought I needed to be medicated out of my pain. But, as she explained, chronic stress and anxiety can alter the chemical balance of your brain. I grudgingly agreed to try. And within two days, the darkness parted and a bit of light shone through. By the end of a week, I had some of my energy back. And not long after, I felt equipped -- mentally and physically -- to cope with my husband's sex addiction, my mother's unexpected death (inconsiderate of her to die just when I needed her most!) and help my three children cope with their grandmother's death and just growing up.
So...by no means am I a pill-pusher. But nor am I anti-ADs anymore. I'm in the process, 1 1/2 years later, of being weaned off. No side effects and I feel good. Which means they did their job.
If you can't imagine ever feeling good again, it's worth discussing the possibility of ADs or anti-anxiety medication with your doctor. I've learned the hard way that asking for help is courageous.