His Everything by Jenika Snow

Ace Renaldo and Lauren Dunn have known each other since high school, and she’s loved him for longer than she’d ever admit. But the darkness that Ace has in his life has changed the boy she once knew.
He’s harder, damaged. Scarred. And she doesn’t know if any amount of love could penetrate the thick wall he’s built around himself and his heart.
To block the pain in his life, Ace fought. He needed the violence as an outlet for the agony he harbored inside.
Before Lauren had come into his world, Ace knew all too well what being alone felt like. She became everything to him, a light in his darkness. But he feared he’s far too scarred to ever be what she deserved.
But she’s everything to him, his entire world, and he wanted to be a good man for her, to love her in the way he always wanted to.
But will giving in to their mutual feelings ruin their lifelong friendship?

Reader note: This was previously published as His Greatest Pain. Although it has been re-edited and parts of the plot tweaked, the story itself is the same.