Why does Quentin commit suicide? Because he's mentally unstable? Because he can't cope with everything that's going on? Because he can't catch up with the changes of society? Because he can't understand how a sister so close to him can become so different? Because Caddy disappoints him? Because his system of values collapses? Because he loses Caddy? (Does he lose Caddy when she strays away from his code of honour or when she loves other guys or when she must marry somebody or when she's cast off by her husband and family?) Because he can't get back to the past when Caddy's his, and innocent? Because she's an unvirgin, not he? Because of his emasculation? Because of his weakness? Because he can't get his sister Caddy back the way the Italian boy gets the little sister back? Because he's unable to fight the guy who has dishonoured Caddy? Because he can't go through with his suicide pact? Because he can't commit incest and can only say it in words? Because his father, instead of being shocked, knows he's lying? Because his cynical father takes the matter lightly and thinks he'll soon get over it, so nobody listens to him? Because he realises that he's responsible for her destruction? Because he feels guilty of being too weak to stand up for Caddy? Because he can't protect her? Because she's no longer his and when she's gone, nothing matters in life? Because he has never had anybody else but her?
In order to find the cause(s) for Quentin's suicide, one must know
what's the relationship between Quentin and Caddy. Yet is it a question
that has a definite answer? Or perhaps it can't be answered, at all?
Whatever the nature of their relationship, there's something so beautiful about it, even if it can be destructive and tragic. I'm afraid putting into words cheapens everything.
Update on 19/11:
2 things in the appendix caught my attention:
1, Quentin commits suicide 2 months after Caddy's wedding, before she's cast off by her husband (and family).
2, Caddy names her child Quentin before the sex of the child is known, and before Quentin kills himself.