Faelan draped all over him made Harry freeze. He wasn't used to having a body so close to his anymore, not unless it was smaller and smelled of baby powder. The motion of Faelan moving past him dragged Harry into the room as well, and he still had enough presence of mind to add his own protective ward to the door in addition to the spells already provided by the Cauldron.
Whether his spell actually worked or not, Harry wouldn't know unless they were attacked, but he couldn't be arsed to care because when he turned around, he was met with the sight of Faelan's back, tanned muscles bunching as the kid stripped off his shirt.