Having been through a divorce myself I can offer up this advice.
1. Do not use the kids as a weapon for any reason. Even if she does, do not do this. Don't talk bad about her at all. If you have some stuff to get off your chest tell it to your counselor but no one else because sooner or later if you talk bad about your wife to anyone else it will end up getting back to the kids and you will end up looking bad in their eyes. If the kids start to say bad things about their Mom put an end to it. You must take the high ground on this no matter what or else you risk damaging your relationship with your kids.
2. Go through an attorney. DO NOT go through the divorce on your own, and make sure every little detail is down on paper. Even if you think it will be a totally civil affair and you think you can trust your spouse to honor any verbal agreements protect yourself. You do not know who is "whispering" in her ear and what they are telling her.
3. Focus on your job and your kids and whatever it is you like to do in your free time. If you are not into anything then get involved in something be it a club, a hobby, an exercise program, whatever so long as it is constructive and healthy on an emotional level and a physical one.
4. Continue to seek support through counseling.
5. Your kids, unless they are infants, are going to go through a period where they think it is their fault in some way. Be sure to reassure them it is not and that they will always be loved by you and their Mom no matter what happens or who they live with.
6. Regardless of what the custody arrangements end up being make sure you are a quality part of their lives.
I must warn you about one thing. How you feel will likely get worse before it gets better. You may feel like you are coming to terms with things and when they papers are signed and the divorce is official you may very well feel like you have went back to step one in your emotional recovery, and you may feel like that again when you end up, assuming you do, living in separate households and one more time when you find out she is dating again. This is all normal so don't think you are not really a man or weak or anything like that.
In some ways men are like Vulcans from Star Trek. We have the same feelings as women, and sometimes are feelings are even more powerful than theirs. We just often do a better job at hiding them than women do.
One thing I can promise you is that there is a light at the end of the tunnel. You can and will get through this. You are not the first to go through this, or the first to be blindsided and sadly you will not be the last. Just take it day by day and know that each day you hold on is one day closer you will be to healing these wounds you have.
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