I know how you feel. I can remember reading the email from the OM. When these things happen the person straying is supposed to be the one to beg for forgiveness, but that's not the reality. I'll try to impart some of the things I learned.
Don'ts
number one you've already been told, do not beg, plead, make promises, or try to be super spouse etc. Do not blame yourself. Do not expect or even hope for some event to make everything right. Any quick solutions will not last, this will take time to heal. Don't physically confront the scumbag boss, it will only get you in trouble. Don't obbsess about your wife's whereabouts.
Dos
Become the best dad you can be, imagine how scared your four year old must be at this time. If your wife comes to you, listen. Any changes you make in your life must be for your growth. Excersize daily start slow if you aren't already in shape, write things, here or in a journal. Talk to friends, but always try and stay focused on your feelings. Expect massive mood swings, these will subside, but it takes time. Set a personal goal for yourself that you have always wanted to do but weren't sure if you could (like a marathon or something similar) then make sure you finish it.
Just remember this is a very uncertain time in your life. You will learn to deal with whatever happens. It feels like your family is gone, but things have only changed nothing is really lost. You can use this for an opportunity to better yourself as a person. If you do that and your wife wants to reconcile then your marriage will be stronger, if your wife doesn't come back then you will still be stronger and now have the knowledge that you can handle things on your own.