Mr. April by Jasmine Garner

Grayson “The Beast,” Childs, a firefighter by day and illegal street fighter by night, falls for Von, a soldier deployed overseas. But when she sustains injuries while serving, he realizes the woman he fell for isn’t the same woman coming home to him.
She feels like a shell of herself, but Grayson is undeterred as she tries to pull away. He’s been that broken before, and knows if he holds onto her, they’ll make it through to the other side.
They connect over their battle wounds, fighting to keep their hearts open as they worry their trauma will eventually tear the relationship apart. Grayson may be a champion fighter, but quickly learns his biggest battle will be outside the ring.
Despite his past, Grayson is nothing but perfect in Von’s eyes. But every time she makes a plan for her life and begins to feel safe, she loses everything. Their relationship should be easy, but she constantly worries that, like everything else, it’ll all come crashing down.