What is the theme in Under the Volcano by Malcolm Lowry?

Every main character n this novel struggles with guilt. The guilt serves as the emotion that holds them back from happiness and success. Guilt haunts from offenses of the past, and escalates when the offended person fails to realize the offense has been committed. For instance, Laruelle feels guilty for his relationship with Yvonne, even though the consul seems ignorant of this fact. Anything that reminds Laruelle of the consul deepens his guilt. Yet, he remains hospitable towards the family.