Dead Reckoning by Maia Dylan

Chris “Ace” Hogan has always trusted his instincts, but the one man who can shake them—Kai Kealoha—has vanished into shadows darker than any mission Hogan has faced. When fragments of memory and scars from Chechnya collide with a hunt for a DEA mole, Hogan realizes the truth he can’t ignore: Kai was his before fate stole the memories, and he’ll risk everything to make him his again.
Kai has lived as a ghost for too long—DEA agent, infiltrator, executioner, survivor. Betrayed and hunted, he carries secrets that could bring down cartels, expose corruption, and destroy the very people he’s sworn to protect. But when his past with Hogan resurfaces, the walls he’s built start to crack.

As the Bratya syndicate closes in, trafficking networks spread, and Black Tide joins the fight, Hogan and Kai must decide if love is their greatest weakness—or the only weapon strong enough to survive the war that’s coming.