Loneliness and isolation
Belinda is defined by her singleness. She experiences insult and injury because of feminist issues in her community which make her disenfranchised because she has no man to arbitrate between her and the community. She is largely rejected by the public, but she does find companionship in another woman whose relationship to isolation is not socially imposed but self-imposed; Lady Delacour refuses to allow others to participate in her intimate suffering so that she is as isolated as Belinda. For a while, they go their separate ways—the loneliest part of the novel to be sure.
Death and sickness
Belinda encounters illness and the likelihood of death in her affection for Lady Delacour. She discovers that Lady Delacour has been hiding her battle with breast cancer from her, and when she confronts Lady Delacour, she finds that death anxiety has worn Lady Delacour incredibly thin. No one in the novel knows how to react to death, so various characters approach it in different ways. The prognosis changes, but the awareness of death and the fear of serious illness prevails until the end of the book as a major challenge that the characters must address.
Friendship
The thematic argument about friendship seems to be a slight criticism of the women and their privacy. When they are closed off from each other, even a little bit, these two women go from friends to enemies. Once their conflict is resolved, the truth is seen; they are are people with whom it is difficult to earn trust. Only time and shared suffering grow their relationship, and the thematic value of this is noticeable in Belinda's sacrifice for Lady Delacour. They are lifelong friends after their near brush with death.
