Oh, Cranbrook, I'm so sorry. I also had infidelity earlier in my marriage. I worked very hard to stay in the marriage--only to be taken down by infidelity again. It is devastating. It really is.
Please know that this has nothing to do with you. I know it's hard to believe, especially when there is a pattern of betrayal. It is tremendously hurtful---and NOT ABOUT YOU. No matter what your wife says. (I don't always use the abbreviations, either, and I've been here for years.)
Right now, you don't have to make any decisions other than those that get you through the next minute, hour, and day. Really, take it in tiny increments, if you have to. Eat as well as you can (if you can't--I couldn't, without vomiting, for MONTHS--find a good-quality whey protein isolate supplement and take a great multivitamin), stay hydrated (but avoid alcohol in any quantity; it tends to make things worse), exercise, rest when you can. If sleep is an issue, as it is for many of us, ask your doctor if you can't get relief from OTC measures like diphenydramine (Benadryl) and melatonin (which works well for some, but can trigger some nutso dreams).
You're right. Your wife has problems. You can't fix them. You can't change a THING about what she thinks, feels, or does---which on one hand is awful, but on the other is tremendously freeing. It allows you to put your entire focus on YOUR OWN healing.
And as unfair as it is, you're wholly responsible for that. She can't do it for you any more than you can fix her. It sucks.
But focus on it. I don't know about you, but the trauma of infidelity created a terrible storm in my mind. Because it was not the first injury of the sort, I really had a hard time---all the puzzle pieces falling into place, the anger, the hurt, the flashbacks to the last time, etc were VERY overwhelming for me. I was very lucky to find an IC who was very brain-based. We didn't do a lot of talking about the past, or the infidelity, or things of that nature---we did some, but the primary focus was calming the neurological storm.
So, we focused on things like biofeedback, breathing, guided imagery, etc. Had these not been effective, she also uses EMDR, a technique VERY helpful for post-traumatic issues. The first things I mentioned can be done on your own--you can find lots of tutorials online, though if you don't have the equipment you can't get the immediate feedback of seeing your heart rate drop that biofeedback software allows. Doesn't matter. It's still happening
I'm not suggesting doing this on your own, without IC. I'm suggesting that my experience with IC--which is not limited to just the one therapist, thought thank GOD she was the one I went to at that point in my life--is that those who are very experienced with trauma and approach things from a physiological, brain-based standpoint can be much more immediately helpful than those who talk a lot. There's a time for that, too. But getting your brain in a good place is an excellent starting point.
One thing I wish I'd done far sooner, with my less-than-remorseful husband, was put the 180 into effect. This technique is described in the Healing Library in the FAQs for BSs. It's #11. It's a series of behaviors designed NOT to change the WS's behavior, but rather to provide you with some distance and detachment (and that brain-calming I already discussed) so that you can more accurately assess your situation. It sounds as though you believe that you are headed for divorce, so getting a head start on detachment is a good thing.
Do know that it is VERY hard to stick to the 180 when you are so acutely injured. It is for everyone. If you slip, no biggie. After a while, you'll learn that each time you engage, it hurts---and eventually, you'll stop engaging.
Gently, I have to bring this up, because it was a huge issue in my family: your 12-year-old knows something is going on. Mine knew before I did--not details, but first that there was something amiss, and then that there was an affair. Even if your child does not know WHAT is going on, s/he knows something is. There's not a right or wrong answer regarding what to tell children--as long as it is not a lie. Be on the lookout for evidence of distress in your child--in mine, it was initially physical (headaches, stomach aches, vomiting). Think about what you will tell him/her--it doesn't have to be detailed, but do be honest. Do not interfere with his/her relationship with your wife, but don't lie to cover for her, either. There are plenty of ways to be honest without being harmful.
(My kids? They're older now, and know a lot more about their father's pathology ---he's personality disordered and really not able to love the way most of us do-- and are very angry and very conflicted about him. My job now is to listen, and now I am FAR more honest about his limitations with them. It's important THEY not feel that any of this has ANYTHING to do with them. Of course, that's their inclination--kids, even grown ones, have a tendency to make everything their fault. It happens whether we like it or not--but it's important to combat it the best we can.)
I know this is overwhelming---the situation AND the wall of words. People here are patient, and I hope you will stick with us. You'll get lots of good support.
You will get through this. It is awful now, but will get incrementally better with time. Healing is sort of a one-step-forward, two-steps-back process----but you will heal. I promise.