Loss of Innocence
Pierre's story is an unfortunate coming of age. At nineteen, he is forced to reconcile his childishly trusting opinion of his parents and his legacy with new information of their greed, corruption, and treachery. This is not an easy leap to make; the news sends Pierre into a spiral of defense mechanisms as he tries to process the feelings alongside the information. As a result of his time in New York, Pierre becomes simultaneously enlightened to the overall danger of the world. He witnesses firsthand the murky underworld of poverty and crime of which he was too privileged to experience at his home estate. On his own, Pierre develops resources in himself in order to defend against this world, but he mourns the loss of the kind, naive, and even gentle young man he was before this endeavor. Experience is willfully thrust upon him at once.
Familial 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.
Escapism
Doubtless due to Isabel's influence as much as his own desire, Pierre continually chooses to run from his problems. He leaves his home for New York after losing his inheritance. He hides Isabel, Delly, and Lucy away from Glen and Lucy's brother and the respective authorities. Huddled into a tiny shared apartment in a low-income housing situation, the four of them create a proverbial haven where the problems of the world are not allowed to enter. They hide away from the crushing pressures of adult life, until they cannot any longer. In a sense the isolation drive Pierre crazy. He is the one to violate those boundaries of safety which the four established for their little haven. Finally, Pierre indulges the most horrific forms of escapism by committing suicide. He loses patience with the world around him and gives up hope after Lucy's unnecessary and sudden death.