It's never over

Marauders

In the third year, on the train, it says that Professor R. J. Lupin is in peeling letters. So its old. Lupin had most likely never been a professor before, and he only knew earlier that summer. So it couldn't be that old. Unless James and Sirius gave it to him. Either as a joke, or a way of saying that even though he was a werewolf, he could do anything.

And then, the compartment. What if the marauders had one compartment that they always sat in. And he couldn't sit in any other, it just wouldn't be the same. And when he opens his eyes, he sees Harry. Harry, one of his best friends son, who looks exactly like him, and thinks for a moment that its James. But then there's the dementor. And he realizes that its only there because of Sirius. Another one of his best friends. Who he thinks, at the time, killed his last best friend, Peter, and is the reason James and Lily died. And then he makes a patronus charm. You need to have happy thoughts to do so.

He can remember a happy thought when theres a dementor, who takes all the happiness out of the room, and if that's not bad enough, its there because Sirius killed Peter and is the reason James died.

Just saying.