lwb. ... I am so sorry. I have been there. Many times I have sat with my kids and watched as my wife leave the house to go out of town to spend nights in a hotel room with her boyfriend. It hurts. It sucks.
You can function. You have to understand that you cannot control him. You can only do what is best for you and your girls. You need to insulate yourself from what is outside of your control. Focus on the kids. Do stuff with them.
It is not easy. I know you can do it. This is where the detachment self-defense mechanism kicked in for me. You will detach, like never before...