Thanks for the feedback. Nathan is a docile, passive friend to Lloyd, who trusts that he is lame enough and scared enough to not do anything with the gun.
But doing something with the gun is precisely what he's demanding at the time! So faced with the lesser of two evils, there is only one choice. I've found that most movies that fail to feel plausible fall down on character motivation, and this is just such a case. Also, the power dynamics of the friendship are not portrayed on screen in the way you set out here.