Infidelity Support Group
Any relationship in which one partner engages willfully in sexual relations with another outside of the partnership is considered to have experienced infidelity. This breach of trust is often traumatizing for the faithful partner as well as the relationship, and support is often needed to heal emotionally and to decide whether or not the relationship should continue after...
That is what you are doing. Take control. Decide what you want. Then go after it.
Your kids are old enough now; you can have a talk with them. You can do family counseling to help them with the divorce. Be an example of integrity and strong moral character for them.
What you allow will continue. Nothing is going to change unless you make some changes.
You are miserable now but you don't have to stay miserable. Make a plan for your life, get a good lawyer, talk with your kids and go for it!