Stiles Stilinski is not that ordinary dorky kid you would take him for if you'd see him, He's smart, It doesn't show, but he's smart. He's smarter than to stay with people who treats him like shit. Apart froom Lydia, he's basically the brain of the pack. But he isn't getting any credit for it of course. So who wouldn't leave? You probably would aswell. But instead of sitting home and being grumpy he takes the thing in his own hands.