Well, I found out today that she has been seeing him since September. It hurts a lot, but this is what I have decided to do.
While I cannot go "dark" entirely because of the kids, I am limiting my conversations with her to texting work schedules, etc. and basic pleasantries when I have to see her in person (dropping the kids off, etc.). I am going to force myself to do this for at least a one month period of time. During that month I plan to work entirely on myself. I am going to get a new look, work out, get my stuff together, etc. When that month is up, I will call her and ask her to meet for coffee or something light. Probably talk about how we'll handle Christmas with the kids. I'll feel things out a bit and take it from there.