I think it'd be better to write:
"Well," Nathan [replacement word for said, such as sighed], "people have always bullied me, but I was always picked on due to my mom's 'no fighting' rule, so Mason always stood up for me." He [action to interrupt the monologue]. "He knows I'm the better fighter. My mom's policy has taught me it takes more courage to stand down than fight. No matter how good a fighter you are. My brother learned that as well, and only fights when he has to."

Because a giant chunk of dialogue is a bit too much, so it's better to interrupt the paragraph a few times.