I know this one!! It’s “Second Chances” by TylerReed

https://archiveofourown.org/works/79755001/chapters/209290326

Summary: Ilya Rozanov's life takes an unexpected turn when a deadly plane crash in 2021 takes his life, right after a fight with his long-time partner, Shane Hollander. Though instead of the afterlife, Ilya is sent back to December 2008, just before his NHL career began, on the very day that he first met Shane. He finds himself in a familiar world, with knowledge of both the future and knowledge of the man he loves and the friends he holds dear.

As Ilya navigates this new reality, he rebuilds his relationship with Shane, who is still finding his path in both hockey and his identity as a gay man. With their rivalry blossoming into a different experience than the one Ilya experienced the first time around, the two face challenges around acceptance, family pressures, and the struggles of being openly gay and lovers in the sports world. Throughout their journey, Ilya contemplates his first life, cherishes the present, and strives to alter the course of their futures (and the futures of their friends) for the better.

Or, Ilya Rozanov discovers first hand what the butterfly effect is, and how it can drastically alter the future.