Regulus didn't know why he had followed you after his prefect rounds, but what he did know was that he was now with you.

The stone floor of the Astronomy Tower was cold and the air damp: he had done well to bring a warm sweater and his scarf. The corpses of bottles that you had stolen from your older brother James were rolling on the floor. You were both stuck against each other, too drunk to get up and go to your respective dormitories. Your head was resting limply on his shoulder and you were shivering gently.

Regulus had been really stupid on this one... what idea to let yourself be dragged by a Pott.er, by a traitor of his blood? However, he couldn't leave you there, in the cold. He gently put his warm scarf around your neck with a clumsy gesture. "Put this on, you can't have a hangover and a cold tomorrow Potter, it would be shameful, even for you"