1. Differences in Opinions: Brutus and Cassius disagree on certain strategic decisions regarding the conspiracy against Julius Caesar. While Cassius urges taking immediate action and using aggressive tactics, Brutus is more cautious and advocates for waiting for the right moment. These philosophical differences may lead Cassius to think that Brutus doubts his judgment and leadership.
2. Brutus's Relationship with Caesar: As the play progresses, Brutus becomes increasingly troubled by the implications of assassinating Caesar and expresses remorse for participating in the conspiracy. Cassius could misinterpret this change of heart as Brutus becoming dissatisfied with the decision they collectively made and, by extension, dissatisfied with Cassius for involving him in such a scheme.
It's essential to note that these suspicions on Cassius's part contribute to the overall tension and mistrust within the conspirators' group and hint at the impending collapse of their fragile alliance.