“Matthias,” she would whisper, his name so soft on her lips. These were the worst dreams, and when he woke, he hated himself almost as much as he hated her. To know that he could betray himself, betray his country again even in sleep, to know that—after everything she’d done—some sick part of him still hungered after her … it was too much.

Matthias narrates these words in Chapter 7, delirious after being treated for his injuries from fighting the wolves at Hellgate. This passage encapsulates the torment that Matthias feels because of his yearning for Nina, which conflicts with his allegiance to his country and what he believes is his calling as a drüskelle. Throughout his imprisonment and despite Nina’s past betrayal, Matthias desires Nina and judges himself harshly for it, gripped by his deep-seated prejudice against Grisha, a doctrine inculcated in him by his training as a drüskelle. The conflict between his love for Nina and the worldview he feels bound to uphold makes him feel disgusted with himself, and he projects his self-hatred onto Nina in spite of his love for her.

Matthias pressed his forehead once, briefly, against Brum’s. He knew his mentor could not hear him, but he spoke the words anyway. “The life you live, the hate you feel—it’s poison. I can drink it no longer.”

Matthias narrates these words in Chapter 35 after betraying his former commander and mentor, Jarl Brum, so that he can rescue Nina. Despite spending much of the novel longing for a return to his old life as a drüskelle, Matthias realizes, through his bond with Nina, that the drüskelle hatred for the Grisha has poisoned his mind. Even so, it still pains Matthias to betray Brum, who has always been like a father to him. Up until the moment he turns on Brum, Matthias feels the strong pull of allegiance to Brum and to Fjerda. Before putting Brum in a sleeper hold, Matthias tells Brum that he doesn’t know if Brum is wrong about the Grisha in general, but he knows that Brum is wrong about Nina. This suggests that Matthias’ love for Nina is his first step towards a more tolerant, and less poisonous, worldview. 

[Nina] swallowed hard. She remembered those words and what they truly meant. I have been made to protect you. Only in death will I be kept from this oath. It was the vow of the drüskelle to Fjerda. And now it was Matthias’ promise to her.

This quote appears in Chapter 37 after Matthias frees Nina from the cell and confesses his love to her. In this moment, Matthias quotes the pledge to Fjerda, but he directs the pledge toward Nina. This implies that his love for Nina has replaced his allegiance to his country. It also illustrates that Matthias understands his love for Nina and allegiance to Fjerda are incompatible—but he has made his choice. In pledging his allegiance to Nina, he is breaking the pledge he once made to Fjerda. In this particular conflict between love and allegiance, love wins out.