Shadows He Feared by Penny Brandon

When threatened with the death of his sister unless he obeyed a specific set of instructions, Oliver thought it a sick joke—until someone murdered his sister. Crushed by guilt, Oliver hid behind closed doors, shutting himself away, unable to trust, unable to face the horror of what he'd let happen.

Aiden loved to bake and give away his creations, but when he dropped off some cookies to his next-door neighbour, he didn't expect to find a terrified man who shied from even opening his door, a man who wouldn't let a stranger close.

Over time, when Oliver finally spoke to him, when he finally smiled, Aiden lost his heart—but Oliver carried a brutal, lingering grief, a shattered soul, and Aiden wasn't sure if his love was strong enough to draw Oliver out of the shadows he feared.