You might consider the theme of family betrayal..... along with Pierre's disagreement with the chaos and darkness of the world, he learns that his own family is infected by these forces. They are not immune to greed and selfishness, despite the security with which Pierre was raised to feel toward them. After meeting Isabel and confronting his mother, Pierre is told that he will not inherit his father's estate unless he ignores Isabel and marries Lucy. Unwilling to accept this ultimatum, Pierre leaves and seeks aid from his cousin, Glen Stanley. Glen joins Pierre's mother in betraying Pierre, even becoming engaged to Lucy at one point. Pierre is on his own; the message is clear. Of the experiences of his traumatic young adulthood, these two most profound betrayals probably contribute most strongly to Pierre's suicide.