The correct answer is the actor-observer bias.
The actor-observer bias (AOB) refers to the phenomenon where we attribute our own behavior to external factors beyond our personal control, while attributing others' behavior to factors internal to them, and fully within their control. In this instance, Tom believes that he is unable to stop gambling due to the negative influence of his friends (an external factor beyond his control), while believing that Barnaby is unable to stop gambling because he is addicted to it (a factor internal to Barnaby). Thus, Tom is demonstrating the actor-observer bias