Never Quite Gone by Greyson Vale

Six years after losing his husband in a tragic accident, Dr. Eli Monroe has mastered the art of existing without living. His surgical hands never shake, his heart never wavers, and his carefully constructed walls never crack. Until the day Alexander Rothschild walks into his hospital and claims they’ve loved each other across lifetimes.
Alex has spent centuries searching for Eli’s soul—through Renaissance Italy, Ancient Greece, and countless lives between. But this time is different. This time, Eli is still wearing his dead husband’s ring. This time, the man determined to destroy their love in every lifetime is watching from the shadows. And this time, Eli remembers everything—except the tragedy that shattered their first life together.
As memories of past lives begin to surface, Eli must confront an impossible choice: cling to the safety of his grief or risk everything for a love that defies death itself. But some patterns are written in blood, some fates demand sacrifice, and some loves are worth dying for… again and again and again.

In this lifetime, they have one last chance to break the cycle. If only Eli can believe that some loves are strong enough to survive both death and destiny.