Girselda is being tested by her husband to prove her worth. Gualtieri is persuaded to take a wife by his vassals and puts his new wife to his test. He feigns to kill their children, divorces her, and even makes it appear to take a new wife. But Grisalda is patient and Gualtieri sees how loyal she has been and rewards her so.
The frame for the Decameron and The Thousand and One Nights is very important. In Thousand and One Nights the stories are being told like parables for people to learn from. To try and change the kings mind and make him realize his errors. The Decameron felt more like a drama to me. With each story teller trying to distract themselves from the plague around them.
In the story Laustic the nightingale symbolizes the love between the wife and the other knight. While its free the lady is happy and is able to love the other night through their windows. When the husband murders the nightingale it not only represents the end of the lovers but of the ladies hopes or fantasies.