Severus Snape was heartbroken. And terrified. Two words that would never be associated with the twenty-one year old potions apprentice. Severus Snape was supposed to be calm, collected, and snarky at all times. However, as he frantically rushed after his lover, Remus Lupin, he was anything but. Remus Lupin was extremely sad, and also extremely angry. The night before, three of his best friends, Lily and James Potter and Peter Pettigrew, had all been murdered. Lily and James were lost to Lord Voldemort, and Remus' other best friend, Sirius Black, had murdered Peter. When Remus found out what had happened to his best friends, he rounded on Severus, the only person, in his mind, who could have known what was going to happen and stopped it. Severus was a spy in Voldemort's inner circle; he had to have known what the Dark Lord's plans were. Remus was convinced that Severus intentionally withheld information from Albus Dumbledore; information that could have saved his friends' lives. He believed that Severus had turned back to the Dark Lord.
Severus came to a stop at the doorway to his and Remus' bedroom, breathing heavily. "Remus, please," he pleaded as his husband threw clothes and random items into his trunk. "Please don't leave… let me…let me explain. I told Albus every…" He stopped as Remus wheeled around and fixed him with a heated glare.
"Don't you talk to me, Snape! Don't you even! Wasn't it enough that you turned to the Dark Lord in the first place? Oh, I know what you say, 'I had no choice, Remus'. There is always a choice. And now… now I see what yours truly was." His voice was pure venom, pure hatred. "You had us all fooled, Albus included!" Remus turned his back on Severus's heartbroken form. The pain and rage were thick in his voice when he spoke again, "And now… now you have caused the deaths of the only true friends I ever had. I will be leaving, Snape, and I would advise you not to follow me or try to find me." He slammed his trunk shut, shrunk it, and immediately apparated away.
Severus, for his part, fell to the ground sobbing, where Albus Dumbledore, Headmaster of Hogwarts School of Witchcraft and Wizardry, found him several hours later. When questioned, Severus would only say that he had made the worst mistake of his life and lost the only thing that ever mattered to him in the process. After Albus left him, Severus too packed his things and left the house he and his husband had shared. No one knew where he had gone and none tried to find him. Years later, when he completed his apprenticeship, he returned to Hogwarts to apply for the Potions position. The wizard that approached Headmaster Dumbledore was completely unrecognizable. Severus Snape had always been a rather cold individual to those who did not know him well, but the Severus Snape that spoke to the Headmaster appeared to have closed away all of his emotions, shutting himself off from the world. Severus Snape, it appeared, had lost himself and as such, his will to live, to love.