Nathaniel wasn't someone weak- he wanted to think that he had some kind of strength. Either as himself, or as Caprikid, he had to have some worth, right? But, then again, he never really could fight back. Not when he was himself.
He couldn't fight back all that time ago, when Chloe took his drawings and ridiculed him in front of everyone. He couldn't fight back when Hawk Moth went ahead and akumatized him, turning him into The Evillustrator. He couldn't fight back when he was accused of stealing that goddamn bracelet. He couldn't fight off the urge to be an asshole to Marc, when he ripped off his notebook and mocked him. Even as time went by, he still felt so, so guilty about that... specially now that Marc was his, uhm...
... No comments.
But, most importantly, he hated how he could never fight back against his mother. Even if he tried, even if he struggled back, he ended up doing pretty much as she wished. Changing his art, and pretending to be someone he wasn't... which, in this case, was by presenting Marc as his...
"Great friend."