What social concern is addressed in the novel, The Alexandria Quartet?

In his head note to Balthazar, Durrell indicates that his primary concern in The Alexandria Quartet is "an investigation of modern love." The range of "modern love" investigated includes everything from old-fashioned "womanizing" to entangled homosexual and bisexual passion, from rape to intricate incestuous relationships, from child and adult prostitution to inverted masturbatory fantasy, from unrequited love to traditional marriages compounded with political intrigue, from simple "loving-kindness" to life-affirming heterosexual relationships based on a "tenderness" which is at once sexual and spiritual.