Ok, time to work on getting through it now. We all knew there was an OW. Deep down you knew it too. Fantasy, emotional, physical, it really doesn't matter.
Time to stop dwelling on the past, what you've lost, and that you didn't deserve this. You aren't special. None of us deserved this.
Now for the good part. You are a very strong person. You are a great mom. You are going to get through this. I firmly believe he will come crawling back some day and I hope he finds a very strong, self-confident woman, who makes the terms for her own life.
It will only be weird for the kids if you make it so. Read Gordie on MLC's earlier post for what his wife did with the OM and having him around the kids. They are in the process of reconciling.
Don't make decisions now about whether and how you would take him back. That isn't on the table and probably won't be for a long time.
Focus on you. Focus on the kids. Focus on your work so you don't have issues there. You don't need to be dependent on this man.
There is a path through this. The ending may not be a certainty, but you will be standing there a more confident person, with a better connection with your kids, and with full knowledge of what you will and will not take in a relationship.
Stop the monkey braining. Stop thinking about what he is doing and with whom. You don't real know the truth. Read BluWave again on what she thought vs. what was really going on.
I am so confident that you are going to be a better person for this. You have all the right ingredients. Know that the people here care about you and will help you get through.