Isaac was pacing down the empty corridors of the institute when he found him, nose unsurprisingly buried in another book as he sat with his back towards the door. Never one to shy away from an opportunity when it presented itself, Isaac slipped soundlessly into the room, not stopping until his mouth hovered mere inches away from Alec's ear.

"--What are you doing?"

The flinch that followed was comical, Alec dropping his book in the process. 

"JESUS! Are you trying to give me a heart attack?!"

When his eyes finally found Isaac's, his breathing had managed to slow down to a reasonable pace. Isaac only laughed in response, placing an apologetic kiss on his boyfriend's cheek, and wrapping his arms around his waist. 

"You're still smiling. I can feel it against my neck, you jerk."

"You have to admit, it was pretty funny."

"It wasn't even--"

Silenced with an impromptu kiss, Isaac grinned against Alec's mouth, teeth tugging on his boyfriend's bottom lip as he withdrew. He pouted when he noticed the look of indignation still being worn by his surprise victim.

"I'm sorry, baby," Isaac began, breaking eye contact in favour of peppering Alec's neck with open-mouthed kisses. Warm hands ventured beneath his shirt, stopping just above his navel to draw patterns along the bare skin. A bold hand dropped lower, fingers trailing through the light dusting of hair as he sucked a mark on Alec's pulse point. He felt Alec shake, stifling a groan behind a bitten lip.

Between the fever-inducing kissing, and burning pathway of his hands, Isaac knew his boyfriend had turned into putty, pliant to his every touch. He pushed down a smug smile born of that particular thought, instead opting to trail a line of sloppy kisses all the way up to his ear. 

"Forgive me?"

"I           "

To punctuate his genuine sentiment even further, Isaac pressed his palm against the front Alec's jeans, teeth tugging on his earlobe as his boyfriend groaned loudly.

"          God, Isaac. Okay-- okay, I forgive you, just--"

Isaac withdrew from the touch immediately, kissing Alec's shoulderblades before returning to an upright position. This time, he didn't bother suppressing the smirk that surfaced when Alec whined at the loss of contact. 

"I'm glad you forgive me. Anyway, I've got training to do, so I should probably get going."

He pressed a chaste kiss to Alec's lips, fingers brushing along his cheekbones as his boyfriend tried to deepen the contact. Isaac broke them apart, a thumb tracing along his jawline as blue eyes gazed on with affection.

"I'll try not to scare you in the future."

Straightening himself again, he pressed another brief kiss on Alec's palm before dropping it to his side. Isaac began walking towards the exit, somehow keeping his poker face on as Alec stared back at him with an amusing combination of confusion and lust. He paused at the doorway, 

"Oh, and babe? You might want to take care of that," he teased with a smirk, gesturing towards the noticeable bulge in the front of Alec's jeans before leaving the room.

"You're the worst kind of person!" Alec shouted at the empty doorway, Isaac laughing as he continued to walk with only a singular thought crossing his mind:

"You know, whenever you leave, I'm always worried you won't come back."

Pressing a chaste kiss to the space between Alec's shoulder and neck, Isaac scrunched up his nose at the taste of filth. It was always like this-- late at night when his boyfriend finally came home from a hunt with his parabatai. 

"It's very distressing. You've turned me into a teenage girl who feels like she's getting ditched on prom night."

"I'm not a very good dancer."

They always made light of how serious the situation is, knowing full-well that either one of them could die at any given moment. Shadowhunters rarely lived past their thirties, after all. It came with the demon-slaying territory. 

Linking his fingers between Alec's, Isaac gave him a quick tug in the direction of the bathroom, his thumb rubbing soothing circles on the back of his palm. Alec seemed dead on his feet; completely pliable to Isaac's touch. Good.

"C'mon. I'll take care of you."

A few minutes later, Isaac locked the bathroom door behind them, a bath already being drawn as Alec leant his exhausted frame against the vanity. Isaac sighed before crossing the room, lithe fingers working at the leather buckles of his boyfriend's vest before tugging down the zip and dropping the offending item to the floor. A fond smile toyed on his lips as he leant down to claim Alec's mouth in a slow kiss, hands working at popping the button of his pants and dropping them to the floor.

"I'm going to have to carry you to the bathtub, at this rate. Aren't I?"

Alec just watched him with a burning gaze, Isaac's insides twisting at the intensity. He felt fingertips brush along his stomach before giving up out of impatience. The pad of an index finger traced along Isaac's bottom lip, Isaac grinning before pressing a soft kiss to its surface. Alec's eyes darkened two shades at the motion.

"Why are you still wearing clothes?"

"Because it's cold. And unlike you, I don't have the adrenaline of a demon fi--"

Alec cut him off with a kiss, burning just as bright as his gaze as his weakened limbs did their best to tug his shirt over his head. Isaac laughed at the insistence, happily removing the material before dropping it into the pile of clothing beside them, and kicking it into the corner of the room. Alec's mouth reclaimed his own the moment the shirt was out of the way, gentle and sweet as fingertips brushed along his chest. Isaac couldn't help but gasp at the sensation.

"You know, this really isn't what I had in mind when I said I'd take care of you."

Alec paused, expression unreadable as he pulled back. Isaac winced at the loss of warmth, his own body pressing closer to compensate.

"You don't want this?"

Isaac shook his head, a smile curving at the corner of his mouth as he moved a hand to rest against the side of Alec's face. 

"You're exhausted. Let me take care of you."

"You don't have to--"

"--Alec. I want to."

Littering kisses along Alec’s collarbone, Isaac withdrew with his nose scrunched up again.

“--after you’ve cleaned up. C’mon. Bath.”

Situated comfortably in the tub, Isaac slipping in behind, Alec relaxed into the position as his boyfriend's hands loosened the knots in his shoulders. When an unabashed groan tumbled from his mouth, Isaac bit hard on his bottom lip to stifle a groan of his own.

"Jesus, Alec. Anyone who walked past the bathroom right now would think I'm fucking you."

A rare laugh fell from Alec's lips as he pressed his back against Isaac's chest, humming contently before opening his bright blue eyes and staring up with amusement. 

"Why aren't you?"

Isaac felt his body light up with want, hands abandoning their place on Alec's shoulders in favour of wrapping around his waist in a tight embrace. He placed a kiss on the back of his neck. 

"God. Vous êtes trop facile d'aimer."

"What did you just say?"

Frozen by the question, Isaac smiled against his skin, tongue darting out before his teeth brushed against the same place.

"...You're the worst?"

"Liar."

Isaac laughed at his indignant response, Alec's amusement plainly written in his eyes. Leaning over his form, Isaac kissed him quickly before gripping him by the hair and tugging his head to the side to expose his neck. His lips teased their way up to his ear, the trademark smirk firmly in place as he tugged on Alec's earlobe with his teeth. 

"Calling me a liar before you've gotten laid? Bad move, Alec," he spoke with a sultry whisper, a hand lightly pulling his dark raven hair as his breath hit Alec's neck. "You're in trouble now."

"We haven't got all nigh--"

Alec's hands immediately moved to grip the edge of the tub, the water sloshing at the speed of the sudden movement as his whole body tensed. With a gasp, his eyes fluttered closed at the sensation of Isaac's mouth on his pulse point, and his hand--

"-- oh god. Isaac-"

Isaac just smirked, dropping his hand from its place in Alec's hair and pressing his palm against his stomach instead. Hearing his boyfriend come completely undone with one of his hands wrapped tightly around his cock-- yeah, it was definitely becoming one of Isaac's favourite things. 

"I warned you, babe," he finally spoke with a laugh, enjoying the way Alec's body tensed and shivered in his hold, coupled with those stupid little breathy grunts that made his own body twist with pleasure. "-- Je voudrais pouvoir vous faire sentir comme ça pour toujours. I love touching you."

Alec moved a hand to grip Isaac's forearm tightly, a touch that would undoubtedly bruise later on. He groaned low in his throat, tilting his face enough to claim Isaac's lips in a messy, needy kiss. That was all of the encouragement Isaac needed to quicken the pace of his hand; the sight of Alec's face flushed red with kiss-swollen lips. 

"--you're going-- to-- kill me."

"But what a wonderful way to go, huh?"

"You're such an assho--"

Alec bucked up into his hand once, twice, three times -- his climax making his body shake as he exhaled a loud, long groan that echoed in the tiled room. 

Breathing heavily with a blissed out expression as he lay spent in his boyfriend's arms, Isaac resumed massaging his shoulders as if nothing had happened a minute ago. 

A knock on the door made Alec flinch.

"I hope you two idiots are done defiling every damn surface in the shared male bathroom."

Isaac laughed as Alec turned beetroot red, his head flopping back against the edge of the bath.

Jace always did have a knack of catching them in the act.