To Prove Worth (слэш)

When twenty-four-year-old Harry Potter accidentally triggers a dark artifact in Grimmauld Place, he's thrown back to January 1982—into a world where his parents just died and his infant self suffers with the Dursleys. Desperate to adopt young Harry, he strikes a deal with Dumbledore: pose as Harrison Burke, prove his stability as Hogwarts' new DADA professor for one year, and demonstrate he won't vanish back to his timeline.
But proving himself means helping someone unexpected—a young, self-destructive Severus Snape who's barely surviving in the aftermath of Lily Potter's death