Just One More Time (слэш)

When a person’s soulmate dies that person can become stuck in a time loop, reliving the day it happens again and again until they find a way to help their soulmate survive. It’s just Harry’s luck that his soulmate apparently died in the Battle of Hogwarts, and he has no idea who it could be.
Or
Harry loops. Snape dies. Until he doesn’t. And then everything changes.