What is the theme in A Severed Head by Iris Murdoch?

One of the main themes in A Severed Head by Iris Murdoch is infidelity. There is such a tremendous amount of infidelity in the book that it is difficult to keep straight who is betraying whom. At first the reader is led to believe that the only person being unfaithful is Martin. The tale ends up revealing that everyone has been unfaithful in some way.