The door had barely closed before the two canids embraced passionately and started to sloppily make out, forcing the taller to fumble the locks closed by memory alone.
Hands swept over bodies as the two horny dogs shuffled and ground their way down the short corridor to the large main room.
Panting they broke the kiss so a tie could be removed in the darkness.
"I shouldn't do this..." Jay huffed, as he lent back to let his lover unbuckle his belt.
"Why not?" Melody responded, panting equally as she desperately fought in the darkness to undo the taller collies fly, cut off by a resumption in kissing as the button and hasp arrangement over her mates bulging crotch finally loosened. 
The conversation was broken as he lent back in, tongue resuming is exploration of the shorter collies muzzle and fangs. One paw slapped at the wall to bring some light to the frantic darkness of their entwined bodies, the other cupped and ran though her head-fur. Finally getting a switch the the recessed lights blinked on in a flair of blue-white LED, causing the canines wince at the sudden illumination filling the apparent.
"I'm getting married Saturday." Jay gasped as his sister broke the kiss to nibble his neck, one hand pulling his head and neck down to her shorter height, the other tracing and loosening his shirt.
"So? Don't you want to fuck your sister one last time?" She panted back, looking up at him, legs entangled as she humped his thigh and he ground against her hip and stomach.
"Of course I do. I always want to. But I shouldn't." He cupped her cheek and moaned softly as her hand slipped into his boxers and gently cupped his balls, pre matting her wrist fur and darkening his shirt.
"Then stop... Tell me to stop. Say no. You know you can." She gasped as he pressed his thigh firmly up between her legs, yanking at her kilt to get a hand up and cup her. As expected she wore no underwear.
"That's not what I said. I said I shouldn't. We shouldn't." He started to massage around her thighs, fingers tracing around everywhere but her sex, teasing her sweet spots.
"But you will, we will. Just as I shouldn't have sex with my older brother, you shouldn't with your pup sister. We still do..." She returned the action, trailing her and over his balls, thighs and crotch, winding him up further.
"Exactly. I shouldn't have taken my pup sister all those years ago."
"I shouldn't have ridden my older brother..."
"But still"
"We do"
Their teasing brinkmanship over the dam broke, white and black border collie muzzle locked to mottled grey-brown and white mongrel border/merle collie.
With a shift, years, over a decades worth by now, of silent unspoken communication as to wants and needs, he positioned himself between her legs. She locked her arms around his neck as with a fumble he held her hip and grasped his cock.
Feeling the familiar miniature cock tip like protrusion of his sisters clit he nestled himself between her outer folds.
With a jerk buck he seated himself, hand moving from cock to his sisters back as he started to drive himself into her. Pants and moans of sexual bliss where muted and rendered hollow as the incestuous lovers committed an abomination against the wall of his apartment.
Short fast hip thrusts slid his cock within her, both desperate for the other.

Six months since he'd proposed almost to the day.
Six months since they promised each-other it would end.
Six days since they'd been on his sofa and nearly jumped each-other in the short time his fiancé went to the corner shop.
Six days since they realised it couldn't end, that it wouldn't.
A promise to each-other to end this broken as he slid his cock into his sisters bare cunt.
It felt so good to be so bad.

"Fuck me... Fuck me Jay... Please, don't stop" Melody gasped as they surfaced for air, she clawed at her brother's pale blue dress shirt.
"I don't plan to... I'm so close. Oh... Melody you feel so,,, good , fuck! I'm close" he didn't care the rough wool of her kilt was itchy at his crotch, he didn't care he'd probably have to dry clean his suit trousers to get the fluids out of them.
His sister was the second pussy he had been in, and his longest partner, most loyal lover, all the way back to being pups.
"Do it, do it big brother! Cum in me! Please, I need it! Cum in your sister, one last night... Empty yourself in me. Please!" She begged as she nipped and nibbled at his neck and jaw. She could feel the unformed lobes of his knot grinding and bumping against her lips, slick with their combined lust. "Tie me. Fuck me big brother, please... One, one last time" she shuddered as a small but strong orgasm cascaded over her.
Six months they'd not touched each-other.
Six months and she'd not had sex, her long term kind-of-not-really girlfriend busy travelling for placement year, her parents busy with work and family preparing for the wedding. She'd not even had the time to get a hookup. Six months knowing they never really said goodbye to a relationship older than she was when it started.
"Going to. Not tie, not here, not now... Going to cum in you, cum with you, my sister, my wonderful... Fuck ... Cub... Pup... Little..." He lost control.
He'd had as much sex as he wanted, sometimes more, with his darling fiancé, but it wasn't the same. Melody was like an addiction to him, and he to her.
"Sis-ter!" he choked out as he bucked a couple of times before locking lips with his sister again, several shots of virile watery collie cum spattering into her unprotected sex.
An ending and a beginning. One last time. One last night.