Cullen and Gabriel are definitely teenage boys. There is a lot of love between them, but like most teenage boys they don't show a lot of affection.... that just wouldn't be cool. A hug turns into a punch in the arm, but regardless, it's meaning is understood. The boys share their clothes and occasionally a room. They get along great. Sadly, after Oslo's death and before Gabriel disappears, he actually cries and worries what would happen to him if he lost Cullen.
I punched my brother lightly on the right arm the way brothers do to show affection, and we walked over toward the car as Lucas pulled up.