I can't believe that the Principal knew about the affair and did not find a way to get those people into separate classrooms. That is not a good situation for the children in the classroom. Even if the affair were going great, teaching is not the #1 focus for those two teachers. This is a very weird situation.
Anyway, I hope things will resolve. I know how deep abandonment issues can be. We have an adopted son, and he's been testing to see what it takes to drive people who love him away for years. It is sad how that affects children.