Sadandscared, I've been where you are, and it's a miserable place to be, I feel for you.
The anger will come, but right now your head hasn't caught up with your heart.
My advice would be to feign indifference. A lot of Sandy's post has some good advice about the 180, but it's a hell of a lot to take on board when you feel emotionally broken.
If you can possibly talk to someone in RL, please do. If you can detach from him then that would be great. Plan breaks for you from the home. My ex told me he no longer loved me, was seeing an OW, which he fiercely denied, and refused to leave the family home. I cried, I pleaded, I begged. I made a total prat of myself. Then, one day, I just stopped. I stopped cooking for him, his laundry, his ironing. I went food shoping for me and the kids. I blanked him, I left the room if he came in. If he started rabbiting on about his day, I yawned, got up and left. Basically, I made his home life as uncomfortable as I could. One night he walked in after another 'working late' day, and saw me all dolled up waiting for a taxi. And I just went out with friends for the night. No explanation, nothing.
Then, I got angry. And I filed for divorce shortly after I threw him and his bin bagged stuff out.
This bit is the hardest bit: it will get easier when he goes, the atmosphere will lift, you will find a strength that right now you can only dream of.
Don't be surprised if DC is picking up on the current tension at home, which resulted in the call from school.
If he doesn't go soon, then tell his family, tell his friends, tell the whole world the truth.
Your focus from this minute is you and your kids, nothing else matters.
Take care