Zachariah, for all his subtlety and manipulations, doesn't hide the hunger from his eyes whenever they follow Adam. Adam can practically feel the heat from those glances on his skin but this is a game they both play and whoever gives in first loses. For a human Adam can be astoundingly adamant and for an angel Zachariah can be amazingly impatient.
Especially when Adam is playing hard to get, citing med school, homework and tutorials as the reason he's unavailable but walks around in very little clothing at the same time.
There are all sorts of things Zachariah could do to make Adam surrender to him but for now he sits on the couch and lets his gaze linger between Adam's shoulder blades, occasionally straying to his naked arms.
He knows Adam can feel his gaze upon him. It's only a matter of time and Zachariah has long since mastered the art of being patient and impatient at the same time.
Finally, Adam closes his books and tilts his head back while rolling his shoulders. He stands up deliberately making it look like he just wanted to do that. Half turning in Zachariah's direction, he can see a sly smile on Adam's face before he walks down the hallway into the direction of the bath and the bedroom.
He doesn't come back.
Eventually, Zachariah grinds his teeth and gives in to his impatience, following Adam.
Adam's on the bed, naked, leisurely stroking his cock. Two can play this game and Zachariah takes his time undressing, putting his clothes away properly.
He lies down behind Adam, throwing his leg over Adam's and kissing him roughly when Adam twists his neck as far as he can. Zachariah's left hand grips Adam's hip possessively, pressing them even closer together.
Adam doesn't like penetrative sex and neither does Zachariah but this, thrusting his cock between Adam's closed thighs feels just as good, no, even better, and Adam gasps softly at the sliding motion. The inside of the thighs is one of the most sensual places on the human body, all thin, soft skin with nerves just beneath it.
Adam's hand finds Zachariah's on his hip and laces their fingers together before taking them down to wrap around his cock. Zachariah laughs quietly and smugly into Adam's neck and licks at the sweat there. Adam directs their motions on his cock, so it's no surprise he comes first, after all he knows best what he likes and what not.
He likes Adam like this, pliant and boneless in his grip. His own climax is...hard to describe with the myriad different ways an angel experiences the world even inside a vessel but the closest would be to say that it gives him an idea why Castiel chose Dean Winchester over all of Heaven.
And Zachariah know that it's not just this carnal act of desire, he has tested that theory anything else wouldn't be efficient, it's Adam. Like now when Adam turns around, touches his face and kisses him so sweetly and softly like Zachariah has never experienced before. It rearranges changes something inside him every time, little by little but for once he's not afraid to lose whatever Adam takes from him with his kisses.
He knows their fates have been long since written. He may as well enjoy this for as long as it lasts, and secretly hopes that it will last a long time.