Bruce's title of The Dark Knight has never been more fitting until now; it'd started as a designation meant to describe his vigilantism and his less-than-savory methods of fighting crime on Gotham's streets. Now, however, it's because he's confined to operating in the shade of the night lest he wish to burn when the sun rises.
And by burn, he means burn. Vampirism runs in the Wayne family like a generational game of roulette, and while Bruce was raised knowing this— that some Waynes were lucky enough to be "blessed" with the super-strength, the enhanced senses, the immortality— he hadn't expected to be one that would experience it. His father hadn't developed the condition, nor had his grandfather or countless others before them, so it's all the more jarring when Bruce develops it after the Gotham Seawalls fall and he stops the Riddler and his plans.
While burdensome to most, someone with fiscal means like Bruce adjusts smoothly. Wayne Tower is fitted with state-of-the-art blackout curtains and tinted windows, he restructures his responsibilities at Wayne Enterprises so that he can remain indoors during the day, and he's developing a sunscreen that can hopefully ward off enough UV light so he can be outdoors during the day uninhibitedly. Blood bags are delivered to his door inconspicuously, and with his work as The Bat taking place at night, his vampirism only works in his favor.
So why can't he so easily fit you into this new stage of his life like everything else? You, his partner who's been so patient with his shortcomings up until his point, feel like a book he can't read; a riddle he can't grasp because he doesn't want to get it wrong and scare you away.
Bruce lingers in the doorway that leads to his bedroom's outdoor terrace, knowing he'll have to return to bed once the sun rises. But he can't, not with you waiting for him like he's not a monster and instead the man you'd loved before. It's not right.
"In a minute," he rasps when you call for him. His kevlar's never felt heavier.