Peter is scared. At 16, he knows better than to admit it to anyone, but he is, all the same.
At the beginning, back all those years ago, he'd had a nervous little voice in the back of his head, one that whispered that perhaps this prank wasn't such a good idea, that detention wasn't desirable, that he didn't want his record marred by whatever the latest caper might be. Need of friendship, however, as it so often does, trumped fear. After a few incidents, he'd learned that detention wasn't so bad, and with any of his friends it was even fun. He learned not to mind, not to be afraid. For the friends who did everything together, detention was just another entry in a long list of group activities.
Slowly, that voice shut down and shut up. It's been years since Peter heard its last pathetic squeakings.
He wishes he'd heeded them, now. When it whispered, "These things can get out of hand," he'd had no idea how right it was. When it said, "stop now, while you still have the chance," he'd kicked it into a forgotten corner and joined his friends. And now it's too late.
Peter knows what to do when he's scared. He surrounds himself with those who are bigger than the fear, those who don't know it. James. Sirius. But now…now, nothing. He hasn't seen James outside of class, it seems, for days, except when he returns from wherever he's been and falls immediately into bed and sleep, without so much as a "Good night!". This new James is scarily distant.
Now Sirius. Sirius is another matter. Sirius isn't safety anymore. Peter doesn't understand. Oh, he knows the how of it. It's the why that stumps him. He doesn't pretend to know much about friendship, or about anything, really, but he does know that friends simply do not do that.
Remus has been used as a weapon. Peter shudders involuntarily. What happens if someday Peter becomes a cog in the machinations of fate as determined by one S. Black? He doesn't like the thought.
Another thought, even less likable than the first, sneaks in. Much as he may be frightened by Sirius' so-called prank, he knows, deep down, that he's still too afraid to distance himself.
Without his friends, he is nothing. That is, perhaps, the scariest thought of all.