I am sorry that you are here but it is the best place to be when going through this tough time. Your W is most likely having an A with the divorced guy. Your gut tells you that and you should always trust your gut.
It’s very important to read up on boundaries and decide if an ea/pa is a deal breaker for your. It is important to show strength through your actions. You can not control her back you get decide what you will put up with through this process.
Give her time and space and focus on yourself and your children. This is a marathon and not a sprint and will most likely take years to unfold. If you put in the hard work you will come out a winner one way or another. Eat right, excercise, read self help books and the rest will take care of itself.
I’ve been at this for three and a half years am almost divorced and my life is about to get fuching awesome. I was as scared and confused as you when I started.