How do Desiree and Armand feel for the three months of their baby's life?

For the first month of the baby's life, happiness suffuses L'Abri, the house where Desiree and Armand live.  Desiree proclaims to Madame Valmonde, "'Armand is the proudest father in the parish, I believe, chiefly because it is a boy, to bear his name."  Armand's behavior has changed as well to show this happiness the couple feel: He does not discipline his slaves in the ways he used to (at first, it was quite harsh, but now, Desiree mentions that "'he hasn’t punished one of them—not one of them—since baby is born.'").  In fact, Desiree's own mood reflects directly from Armand's:

Marriage, and later the birth of his son, had softened Armand Aubigny’s imperious and exacting nature greatly. This was what made the gentle Désirée so happy, for she loved him desperately. When he frowned she trembled, but loved him. When he smiled, she asked no greater blessing of God. But Armand’s dark, handsome face had not often been disfigured by frowns since the day he fell in love with her.

However, this happiness changes when the baby turns three months old.  Madame Valmonde suspected something was amiss when she visited Desiree when the baby was one month old: 

Madame Valmondé had never removed her eyes from the child. She lifted it and walked with it over to the window that was lightest. She scanned the baby narrowly, then looked as searchingly at Zandrine, whose face was turned to gaze across the fields.

Madame Valmonde is comparing the baby's skin color to that of Zandrine, the nurse who is of mixed race, a term that in Chopin's time and in the South were called "mullato."  Two months later, Desiree begins to notice what Madame Valmonde noticed; her baby's skin color is close to the same color of Zandrine, but Desiree and Armand are both of white ancestry--or so they thought.  When Armand realizes that his child, the boy who would carry on the Aubigny name, is of mixed race, "[h]e thought Almighty God had dealt cruelly and unjustly with him; and felt, somehow, that he was paying Him back in kind when he stabbed thus into his wife’s soul. Moreover he no longer loved her, because of the unconscious injury she had brought upon his home and his name."  Armand thus returns to his fierce manners, horribly mistreating his slaves and basically kicking Desiree and the child out of the house.