Poor Brief
He's a total nerd, but if he cleaned himself up, he'd totally be able to land other people. I mean, other people that aren't Garterbelt - he's already got that down. But he won't fucking do it because he loves Panty, and Panty loves him too, in her own way, but her love isn't exclusive, because her life is about sex. If Brief just went around fucking other people while still fucking Panty, it'd be much more balanced, but he's decided just Not to Do That.
Man's a One Love One Life type guy in a relationship with a woman who's fucked a good portion of the entire population of the city she lives in.