BluDiamond

In September of 1981, a month after they broke up, Remus is playing a guitar and remembering how he and Sirius got together and how they were torn apart.

Why did Sirius tell Snape how to get past the Whomping Willow, putting Remus in danger? Knowing Sirius and his short temper, he must have been angry at Remus for some reason. This is my interpretation of the events of that night, and the following morning.