Nettie runs away from her childhood home because she is afraid of Pa's sexual advances, although Nettie feels guilty abandoning her stepmother to Pa's abusive ways. Nettie joins Celie and Mr. ____ in their home nearby.
Nettie escapes Pa's advances only to find herself in another environment—Mr. _____'s house—in which she will be sexually propositioned, mistreated, and from which ultimately she will be forced to leave.
Celie reports that Mr. ____ still "has eyes" for Nettie. Nettie continues studying for school while in their home, and Celie attempts to control Mr. ____'s unruly children, who typically do not listen to her or obey her.
Celie is a good mother—she does what she can for Mr. ____'s children because it is her wifely duty—but the children simply hate her, perhaps because they feel she has replaced their mother, who was murdered by a lover.
Mr. ____ continues to make advances to Nettie, and strongly implies that he wishes to have sex with her. Nettie refuses Mr. ____, thus angering him. Mr. ____ tells Celie, as a result of Nettie's refusal, that Nettie must leave their house. Celie gives Nettie the name of the Reverend and his wife—the only people, Celie says, she has ever seen with money. Celie tells Nettie to find them in Monticello and to ask to stay with them.
It seems hard to believe, but it is in fact true, as far as the narrative goes, that Celie has never seen money, nor has she had occasion to spend it. The day she once passed in town, observing Corrine and Olivia, is perhaps the only time in her life she has been permitted to see other people going about their business. Mr. ____ keeps Celie, essentially, as a maid in his house, and as a nanny to his children.
Nettie is happy to leave Mr. ____ and his "rotten" children, but feels guilty to leave Celie. She promises Celie she will write to her when she reaches the house of the Reverend and Corrine. But, Celie says, in this letter to God, that Nettie never does write.
One of the novel's great unbroken promises. Of course, Celie does not discover Nettie's letters, hidden by Mr. ____, for some time. But Nettie does in fact manage to correspond with Celie over the span of many years.