Final answer:
The main theme of the passage is the betrayal by friends, as it centrally revolves around the protagonist being betrayed by trusted individuals.
Step-by-step explanation:
The main theme of the passage focuses on the betrayal by friends, given that the individual in question is betrayed by those he trusted. While the importance of reading and underground press are elements in the passage, they serve the plot rather than the overall message. The need for trust could also be a part of the theme, but it is the outcome of the trust (which is betrayal) that is central to the character's conflict.
Thus, the most fitting overall theme is the betrayal of friends. Understanding themes in literature involves looking beyond the surface details to grasp the deeper meanings and messages that authors incorporate into their works, often conveyed through character interactions and plot developments.