The night before his first birthday at Hogwarts Sirius stayed awake not out of excitement, but fear.
He remembered the morning of his ninth birthday far too clearly. He had been woken up with hexes and curses that made it feel like his skin feel was on fire and his bones were being shattered.
Every year from then on he was woken up on his birthday by the all-too-familiar sense of pain. His eleventh birthday was the worst. His parents knew that he wouldn't spend any more birthdays at their house, so they had to make this one count. As a "special treat" they woke him up using the cruciatus curse. This continued for half an hour when he finally passed out from the pain.

On his twelfth birthday Sirius woke up at half past five and crept out of the dormitory, cringing when the floorboard by the door creaked, terrified that he would wake up Remus. He sat close to the fire hugging his knees, dreading the moment James, Sirius and Peter woke up, terrified that they would continue his birthday tradition.
Remus was the first of the other three to wake up. He noticed that Sirius' bed was unusually empty for 6:15 in the morning. Remus walked downstairs and saw Sirius by the fireplace. Hesitantly, he sat down next to Sirius who flinched away.
"Please don't hurt me. I'm sorry. I didn't mean to do it."
Remus was confused. In the short time he had known Sirius, he had learned that Sirius rarely apologised and didn't often shy away from people.
"I won't hurt you. Why would I? Today's your birthday isn't it?"
Sirius nodded slowly, fear still in his eyes.
"I got you a present," Remus continued, "James and Peter have presents for you as well."
At home a present usually meant a curse or a hex or a chore generally reserved for Kreacher, but there was something in Remus' voice that made Sirius trust him.
Remus handed Sirius a neatly wrapped box. Inside was a photo album with "The Marauders" hand written on the front.
"I thought we could add photos and stuff for when you have to go back home so you know you will always have us with you." Remus said softly, playing with the sleeves of his jumper.
Sirius smiled and thanked Remus. "That's the nicest thing anyone has ever done for me."