Final answer:
Marcus is struggling with feelings of jealousy and internal conflict due to a romantic rivalry with his best friend, McTeague, over the same love interest, Trina.
Step-by-step explanation:
The character Marcus exhibits signs of being uneasy and out of temper which could allude to a sense of jealousy or internal conflict. Specifically, Marcus finds himself in a difficult situation because he and his best friend, McTeague, are both presumably in love with the same girl, Trina—Marcus's cousin. This love triangle puts Marcus in an awkward position as he battles between wanting to be a supportive pals and the bitterness of rivalry. Additionally, the nuances in the interaction between Marcus and McTeague often indicate underlying tensions, further compounded by Marcus inviting Trina to see McTeague about her tooth—an action that advances the story and entangles the characters deeper into their interpersonal complications.