How did others treat her differently because of their suspicions?

After Désirée's baby is born, her mother finds it hard to think of her daughter with a baby. Now, not having seen her daughter for a month, Madame Valmonde is eager to visit Désirée. When she looks at the baby she exclaims, "This is not the baby!" Désirée thinks her mother is amazed at how he has grown.

Madame Valmonde 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, [a light-skinned slave] whose face was turned to gaze across the fields.

"Your child has grown, has changed," she remarks to Désirée. Then she asks what Armand thinks about him. Désirée replies that he is very proud of his baby. Later, however, when the baby is about three months old, Desirée feels that there is something wrong because there is "an awful change" in her husband's manner, and she is afraid to ask him to explain. As time passes, Armand's attitude becomes worse. When he is with her, his manner now has greatly changed, and Désirée is afraid to ask him to explain. For Armand speaks to her with his eyes averted, the old love-light in them gone. Worse than anything else, he avoids his child.
Finally, Désirée comes to understand the looks on her mother's and husband's faces and the changes in the attitudes of others. One sultry day, Désirée's absently looks at the little quadroon boy who fans her baby. She looks back at the baby, then again at the boy. "Ah!" she exclaims involuntarily and feels chills. Shortly after, her husband enters the room, and Désirée asks him to look at their child and tell her what it means. Armand cruelly replies, "It means," he answered lightly, "that the child is not white; it means that you are not white."