Needleman: I am sorry to hear your story and I feel your pain and worry.
A primary component to getting through these issues is maintaining strength - the ability to turn the fear, desperation, and sadness around so that you can manage your marriage and your life.
If you want to save the marriage (and your sanity) then you must maintain the strength to make demands. And those demands are unequivocal - regardless of whether she walks out the door. That is what we all say on a routine basis - to save the marriage you must be willing to lose the marriage. And guess what? She's already had one foot out the door and, just so you remember, either way YOU WILL BE FINE. Read that again: you. will. be. fine.
Take a deep breath. Sit her down. Make a list of absolute requirements:
1. There is no contact with any of the other man. Period. Ever again.
2. She begins IC (as do you, btw).
3. She gives you 100% complete and open transparency.
That is the beginning.
If she hems and haws, refuses, isn't sure, "wants time".... etc. - no problem. You refuse to be a third wheel in your own marriage and you let her know that you love her, want her back, but will not be married to someone who is involved with someone else. And let her leave. Let go of the outcome and know that you will be fine.
This provides an opportunity for several things to happen: she can decide if she wants to stay married to you, you can decide if you want to stay married to HER, you can begin the process of rediscovering your own personal strength, you can get your financial and marital ducks in a row by seeing an attorney to know your rights, and it demonstrates to your family that you will not be treated like a doormat.
Have strength. Know that others have made it through this horror and that you will, too.
Good luck and be strong!