I wrote this story following a questionnaire/poll I ran on this site and a few others asking readers about certain character details and circumstances they wanted to see in a story. Here's what I came up with based on the various answers. I really hope you enjoyed how this first part turned out. I'd like to continue this story and hear about where you might want it to go, so feedback and thoughts welcomed and encouraged.
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“Hey, where have you been?” Matthew stopped his shaking leg and jumped off the couch when his fiancée strolled through their front door. “Are you alright?”

“Of course,” Coral said. She flashed him a warm smile and his heart slowed as she slipped off her tennis shoes. She appeared unharmed and completely at ease, and he felt ashamed over his concern, chastising himself for worrying about her. If anything, she seemed refreshed, not as tired as he thought she might have been. “I was at the gym, silly. You know that.”

“Right, yeah,” Matthew leaned forward to give her a kiss on the cheek and noticed she lacked the usual sweaty scent she came home with after working out. She collapsed onto the couch, and he sat down next to her, his posture much stiffer than her leaned backed, relaxed position. “You’re just later than you usually are, that’s all.”

“Mmm, yes, Tyson put me through quite a session today.”

Coral extended her legs onto Matthew’s lap, and he placed a hand on her shin. The mention of her trainer made him feel protective and he wanted to touch her and reassure her. He again regretted his instinctual concern but years of religious upbringing and smalltown living was hard to break, even though he’d been trying. He remembered when Coral first told him about her trainer and showed him a picture of them together, his heart skipped a beat and he stuttered out a question about her safety, about being alone at night with someone like that.

“What do you mean ‘someone like that?’” she had asked with narrowed eyes, and Matthew instantly felt ashamed. They both knew what he meant but it wasn’t just because Tyson was black. It was because he was also huge. He knew personal trainers were usually really ripped but Tyson bulged with muscle like someone sculpted him out of onyx. He also towered over Coral, his small girlfriend barely coming up to the dark man’s chest. However, even that was thrown back in Matthew’s face when Coral added, “Would you be so concerned if he was white?”

The sad truth is that he wouldn’t have been, even with all those muscles and the shaved head. So, he pushed his concerns aside. But he couldn’t help them popping up every now and then. Even though there was no arguing with the results of Tyson’s training.

Matthew’s eyes traveled up the denim clad leg of his fiancée to her trim waist. There was about an inch and a half of space between her slim stomach and the waistband of her jeans, a clear representation of the weight she lost since beginning her private nighttime workout sessions.

Coral was never fat, nor was she really pudgy. When Matthew first met her, she was just shy of average, but it was almost impossible to even tell with the way she dressed. Long skirts and buttoned up blouses hid her figure, but her conservative style made him feel like he had a chance and he approached her and asked her out. Little did he know then what a knockout body his girlfriend possessed. The first time he saw her naked, his eyes nearly fell out of his head. Large breasts that sat proud on her chest; an hourglass shape; a round butt; and a bush that matched the fiery hair on her head.

Now of these days though, it was a little easier to tell how attractive Coral was and she was even hotter now than then. During the last year of high school and into college, she got into more sportier activities and changed her fashion along with it. Gone were skirts and blouses and in were tight jeans, t-shirts, and tank tops that showed off her incredible bust. Then, once she met Tyson and started really working out, her waist got even slimmer, her butt even firmer, and her bush disappeared for convenience.

Matthew was excited to marry and sleep with the girl he first met, but he dreamed of making love to the stunning beauty he was engaged to. Because while they’d done a few things since getting together, they still hadn’t had sex, that religious upbringing once again rearing its pious head. He’d seen her naked, she’d given him numerous handjobs, and even put his dick in her mouth a couple times, like the night he proposed, but that was as far as they ever went.

“Are you going to hop in the shower?” he asked, patting her leg. “I can reheat our dinner once you’re done.”

“Oh, I already showered.”

“You did?”

“Yes. Tyson and I showered at the gym.”

She said it so simply, like it was nothing, and it probably wasn’t, he told himself. Certainly, she didn’t mean it in the way he thought she did. ‘Tyson and I’ meant they just both showered, not—

“T-together?”

“Uh-huh,” she said, and his stomach spun upside down. Her and Tyson showered... together? His mind couldn’t comprehend it for a second but then it hit him like a punch right to the gut. He couldn’t believe this. That she would do something like this. Why did she seem so calm? It must be some sort of misunderstanding still.

“What do you mean you showered together?”

“It’s not that big of a deal,” she said, though from the way her cheeks flushed he knew it was at least some sort of deal. “We went over on our workout, and I was so sweaty and gross that I just needed a shower. But I knew you’d get concerned about how long I was gone, so Tyson suggested we shower together to get me back home faster.” A small smile crept across her lips. “Well, he more insisted. Tyson doesn’t ever really ‘suggest’ anything.”

Matthew listened to his fiancée explaining showering with another man in stunned silence. The moment she admitted the truth, an image popped into his head, a flash of Tyson and Coral naked in the shower together, their bare bodies in close proximity. He felt sick. He felt appalled. He felt... aroused. He squirmed uncomfortably in his seat.

“I—” he licked his lips, trying to moisten his suddenly dry mouth. “I don’t understand. You saw another man naked.”

“Yes, but, people at the gym shower together all the time. So, what if it’s a guy? It’s not like I’ve never seen another guy naked.”

In his mind, Matthew knew it wasn’t the same. The other guys she’d seen naked were her handful of previous boyfriends. Guys she had a relationship with not a well-muscled black man. Again, his cock responded involuntarily to the idea of his girlfriend seeing her trainer naked. Tyson’s blackness was once more affecting him, but in a very different way he wasn’t expecting.

“Plus,” she continued, her voice taking on a secretive lilt, “I was a little curious. Would it be any different... with him being black?” Her legs shifted in his lap, brushing against his erection, and she gave a silent gasp before grinning widely at him. “I guess I’m not the only curious one.”

The sensation of his fiancée’s leg rubbing against his prick made him shiver, almost as much as her admission of wanting to see Tyson naked, except where one brought pleasure the other brought pain, and the two somehow mixed into a dizzying cocktail.

“Was he... it’s just like any other guy, right? It doesn’t matter... him being black?”

Coral bit her lip and shook her head. Closing her eyes, she rubbed her leg across his cock, caressing it through his pants.

“I know I always said it didn’t matter him being black,” her chest rose and fall as she spoke, her breathing growing deeper, “but I was wrong. He’s not like any other guy I’ve seen. He’s so… big.”

She bent her knees, bringing her shapely thighs together and rubbing them against each other. The position placed her feet right onto his cock and she used them to massage his dick as she kept talking.

“Big build. Big muscles. Big... everywhere.”

Matthew groaned from a combination of arousal and heartbreak. Hearing her talk about Tyson filled out the gaps in his imagination of the two of them in the shower. He clearly saw his girlfriend’s eyes roaming across Tyson’s naked body, taking in his dark, wet skin, the shape of his muscles, and though she didn’t explicitly state it, the size of what lay between his legs. And right next to his coal dark body, Coral’s own porcelain white one. Big breasts dripping with water, pale pink nipples hard. Two attractive specimens together, naked to each other’s eyes.

“Y-you just showered together, right?” Matthew croaked out, trying to convince himself that it wasn’t a betrayal if nothing happened. If they didn’t do anything sexual. “That’s all?”

Coral gazed at him, her eyes glassy and lidded. Her feet continued to move at a steady and deliberate pace, slowly masturbating him. “We just showered but I did help him out.”

Matthew’s cock jumped and he scratched his nails across the couch cushion, a dribble of precum soaking his underwear.

“We needed to go fast, like I said, because I didn’t want to upset you.” The implication of this all coming back to him and his own insecurities made Matthew even more confused. But one head was too muddled to think about it and the other head enjoyed it too much to bother. “He asked me to help him wash some harder to reach places and I didn’t want to come off scared or bigoted.”

Matthew’s heart slammed against his chest, his stomach sank and spun, and his mind screamed in perverse agony.

“I started with his back. It was so hard and just lined with muscle. It was like rubbing my hand across stone. I really had to press hard and feel him.” He pictured his girlfriend’s hands against Tyson’s skin and the contrast made him throb. “I did his lower back next and then... I knelt down to get his legs. I ran my hands up and down his calves and then up to his sculpted thighs. He always talked about the importance of leg day, and I could see the effect going up the back and all the way up the inside.”

His future bride on her knees behind Tyson, hands moving up his leg, all the way to where they met, her fingers brushing against the massive shaft between them, but still higher she went until the back of her hand met his balls. Matthew was almost panting in twisted horny agony. Coral’s rubbing and jerking of his cock with her feet had grown more aggressive and intense, bringing him closer and closer to the edge.

“After that, there was only one place left to go.” She paused in her story, and they stared at one another, Matthew’s eyes going wide. Her expression remained heated but calm, trying to emphasize a casualness to what were clearly inappropriate actions. Where was it that was left? His cock? His balls? Matthew opened his mouth but then she continued, cutting him off. “I used both hands to massage and wash his ass. It was so firm, and I wanted to do a good job. I think I did.”

Matthew’s mind filled with the vision of Coral’s white hands squeezing and groping Tyson’s black ass, rubbing all across his muscular globes. He twitched in his seat, humping against his fiancée’s feet.

“I even made sure to get between them, rubbing my hand all the way across his crack to his taint and then back again and again.”

Matthew exploded, cum rushing into his underwear and pants, as he came to the thought of Coral vigorously washing her black trainer’s butt crack and taint. He came more than he ever had before, six gooey spurts of jizz soaking his crotch, all over his white girlfriend molesting and caressing another man. Coming down from his high, his breathing slowed back down to normal.

“So, yes, I showered already,” Coral said, returning her legs to their stretched-out position and her voice to its normal bubbly state. “Are you ready to heat up dinner? I’m starving.”

In a bit of a daze, Matthew got up and headed to the kitchen.
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What would you like to see happen next? I have an idea about Matthew deciding to join Coral and Tyson at the gym, but let me know in the comments if there's anything you'd like to see happen.