Margaret's affair was years ago. You can begin to breathe freely after awhile, can't you? No one will ever find out. But the confluence of a holiday party, alcohol, the flu bug, a game of "Truth or Dare," and irritation with her husband, caused Margaret to blurt it out in front of him and their entire circle of friends. Don't you just hate it when that happens?
Pam blindsides Jack telling him that she is getting a divorce. He isn't making enough money. Jack is much more than Pam or her mother realize. He decided to give wife and boyfriend some bad experiences. In the end he gets what he wants. In the middle too.