#1 Promises of the Night

The demon's name is Sam. Actually, he's Sammaal, after his mother's dead lover, but you can't very well say that in school. The human's name is Gabe, short for Gabriel, after his father's favourite author from when he was younger.
They meet in middle school. Gabe was the only boy in their class who would talk to him, because Sam has red eyes that turn blue when he is scared and horns in his head, peeking over the top of his hair. Gabe, despite being the son of a pastor, did not care. He just wanted someone who would play Pokémon with him. 
Gabe grows up to be a baseball player in high school. Sam goes to all of his games.
Sam only starts to think about Gabe's mortality when they are 17. His body can age at will, but Sam won't ever die. Gabe will. This gives Sam a lot of unwanted thoughts. It is like he is grieving him already. So he asks for advice. 
Sam gets in touch with Jim Sanders, a warlock living in the city, who tells him that the only way for them to stay together for all eternity is for them to bind their souls together, but this is very difficult magic that would take Sam centuries to master. On top of that, Sam refuses to endanger Gabe. He does not want to involve him. So Jimmy offers a second choice. He could exchange his soul for another, trade himself for someone else so Lilith would be happy.
This, Jim tells him, would mean killing someone else and condemning them to an eternity in hell in exchange for Sam's soul and mortality.
The story explores how far Sam is willing to go for his own happiness. It deals with morality, black and white, good and evil. Gabe is with him every step of the way, but he is not on board with the idea of killing anyone unless they are someone truly evil, someone who really deserves to go to hell.