AUTHOR'S NOTE: This story contains gay male sex, as well as straight sex. If that's not your thing, be warned.
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Dan's girlfriend had been acting strange lately.
At first, Shelby was just... kind of distant. He figured she was just having a tough time at work. Being one of the city's top lawyers meant lots of nights spent out late preparing for cases, dealing with difficult clients, or dealing with internal issues at the firm where she was a partner.
Shelby brought home lots of money, more than enough for them to both live comfortably in the apartment they shared, especially since they didn't have kids. Dan didn't need to work, so he took the chance to stay home and write novels, which had found only a small amount of success. He wasn't exactly bringing home the bacon, so he wasn't about to bug her about her job. She was probably tired, and just needed some time to herself.
But after a couple of weeks, he wasn't so sure anymore. What had been some less-than-sparkling conversation and yawns at the dinner table turned to almost complete silence. Sometimes, days would go by without her saying a word. When she did speak, it was a muttered "Good night" at bedtime, or a distracted "See you later, hon" as she went out the door for work. But it wasn't like she was giving him the silent treatment. She wasn't angry or seething. In fact she seemed to be feeling not much at all. At home everything she did was listless, and her face seemed to take on this permanent placid look, and a blank stare that only seemed to lift occasionally when she would pull out her phone and read a message.
Shelby had also started to stay out late more often. Because of her job, late nights were pretty common, but now there were weeks where she would come home every night after Dan was asleep. Once or twice, he even woke up to her talking quietly in her sleep, though he could never quite make out what she was saying.
They weren't exactly the most passionate couple, but after six years together, things began to settle into a comfortable, if slightly monotonous rhythm; one that Dan had started to enjoy. So after weeks, all this behavior had the effect of making Dan extremely paranoid. Was it something he did? Something he wasn't doing? Did he forget a birthday? Or was she...
No, of course not. She would never cheat on him. Then again, Shelby had changed a lot over the last few weeks. It was all of this that made Dan do something incredibly out of character.
He was going to stalk his girlfriend. He rented a car, and parked it a block from their apartment. Then, the next morning, he snuck out right after she left for work and tailed her to her office building. He drove to a coffee shop just across the street and got a table by the window so he could watch for her car leaving the parking lot.
***
Dan knew this was going too far, but he needed answers. This was all just too weird. Because it wasn't just the paranoid getting to him. It was the horniness too.
This wasn't a fetish thing, he was never into all that cuck stuff. The thought of Shelby sleeping with another man--or worse, being in love with him--tore him apart. But in spite of the constant depression and anxiety, he had been horny as hell.
Dan and Shelby usually had sex once a week (if they weren't too busy), and every so often Dan would pull up Pronhub and jerk off if Shelby wasn't in the mood. But over the last few days, he had been hard almost constantly. And since he was still working from home that meant he was masturbating constantly, too. In bed, after Shelby left for work, on the couch, in the shower. He didn't even need porn. He would just stroke and cum and stroke and cum.
It started a couple of weeks into all of this strangeness. Their sex life had dried up completely, along with any affection from Shelby. But one night, she had woken him up late at night after what she said was a tough day at the office. After turning on the lamp, Dan saw that she was kneeling over him, completely naked.
Her gaze was intense, almost manic, and she was biting her lip in the way she did when she was really horny. Without having to look, he could also tell she was fingering herself by the slick sound of her fingers and the feel of her pussy dripping onto his leg. Dan darted up to kiss her, his dick already throbbing in his boxers but she stopped him with a hand on his chest and shoved him back down on the bed.
Without saying a word, Shelby urgently pulled off his underwear and took Dan's 6-inch cock inside of her in one motion.
Their sex was usually pretty vanilla. Nothing too rough or kinky, but they were both happy with it, or so Dan thought. But that night, Shelby rode him like a jackhammer, her pussy gripping his cock tighter than he had ever felt.
"FUCK, YES YES YES YES!" Shelby yelled as she rode him, both her hands kneading her little, pert breasts and tweaking her pink nipples. She was usually pretty quiet during sex too, but Dan wasn't about to complain about any of this.
In almost no time at all, Dan felt himself about to orgasm.
"Fuck babe you're about to make me-"
"OHHHHHH FUUUUCK!" Shelby moaned, seemingly paying to attention to him at all. Seemingly she had beaten him to it. Dan felt her pussy clench even tighter in orgasm, pushing Dan over the edge as well. After her orgasm subsided, Shelby pulled herself up off her boyfriend's cock.
"Damn Shelby, where did that come from?" Dan asked, after taking a few breaths to recover. No response. She had already fallen asleep.
***
Dan hoped this was the end of their dry spell, but the next day Shelby was back to basically ignoring him. That was the last time they had sex, and Dan's dick had barely gone soft since.
Even now, as he sipped his coffee and watched for any sign of Shelby's car, Dan discreetly palmed his erection through his pants. The only thing stopping him from going to the bathroom to jack off was the fear of missing her leaving work. At the very least, he hoped she would leave before the precum he could feel starting to moisten his underwear started to show on the front of his pants too.
Dan was never a big precummer, but with his newfound libido came a cock that leaked like a faucet whenever he played with himself even a little. When he did cum, his loads were bigger too. And they seemed to stay that way no matter how many times he came during the day.
He could barely take it. Dan's cock was screaming for attention and a tiny wet spot was starting to form on the crotch of his slacks. Maybe he didn't need the bathroom. The place was empty except for him and the barista who had only looked up from his phone to make Dan's coffee. He could just pull his fly down and discreetly masturbate while he waited.
After all, he had taken to jerking off silently late at night, while Shelby was asleep in their bed next to him. Usually, he would just excuse himself to the bathroom or his office to do it, but some nights he would wake up unbelievably turned on, his hand already playing with his dripping cock. He would reach down, stroke his erection, and shoot ropes of cum all over himself while Shelby snored next to him.
Though some nights, Dan thought he could hear her talking in her sleep again. Some nights, while he stroked, he could swear he could hear Shelby... murmuring something... over and over... on and on... that just made him so fucking horny. So horny that even the memory of would give him no choice but to get naked and-
Dan shook his head and caught himself with his pants unbuttoned and hand around his exposed cock, precum leaking onto his seat. Thankfully, he managed to regain control of himself before he got completely naked. And he was even more grateful that the barista hadn't noticed anything. He had been zoning out every so often lately as well, he realized, as he gathered all his willpower to tuck his cock back into his pants, which were now almost soaked with pre. Something fucked up was definitely happening, and it wasn't just happening to Shelby. He had to get to the bottom of this soon. And luckily, it seemed like he wouldn't have to wait much longer as he spotted Shelby's exiting her building's parking lot.
Dan left a sizable tip on the table and rushed to follow her.
***
After following her for 20 minutes or so, Shelby's car finally came to a stop in front of what seemed like a perfectly normal house in the suburbs. Parked a block away, Dan watched Shelby exit her car and let herself in the front door. She had changed at some point and instead of her usual pantsuit she was wearing a pair of tiny cotton shorts and crop top that barely covered even her tiny, perky tits. Dan had no idea she even owned any clothes like them before.
After taking few minutes to steel himself, Dan got out of the car and made his way to the house. He felt his heart beating out of his chest, getting more and more anxious the closer he got to the house. But with every step he took, he also felt his cock throb and leak, getting hornier and hornier as he approached the door. Maybe he should have just finished himself off at the coffee shop, but it was too late now.
Dan raised his fist to knock on the door, but found that Shelby hadn't closed it all the way. He took a deep breath and opened it. The sight that greeted him confirmed his fears.
The door opened right into the living room, where Dan saw a massive, muscular man, completely naked, though Dan couldn't see his cock, because it was currently buried to the hilt in his girlfriend's mouth. She gazed up at the man with what seemed like adoration, with her shirt pulled up revealing her breasts, and one had in her shorts.
"Ah, you've finally joined us," the man said. His voice was deep, dripping with smugness. Then again, he probably had a reason to be smug. Dan considered himself average when it came to fitness, but he never had any issues about his body. But standing in the same room as this titan just made him feel so small.
Dan's heart sank. She had been cheating on him all this time, he should have just left her from the start. For the first time he felt his anxiety recede and anger well up in its place. That bitch. She could have just broken up with him. Why did she have to do it like this? He wanted to yell. To let out months of fear, anxiety, and anger.
But he couldn't speak. He couldn't even move, he realized. He was stuck in the doorway, seemingly unable to control his own muscles.
"Sorry you had to find out this way, bro," the man said. "I was going to just take her and run, but this little slut spoke so highly of you. Isn't that right, slut?"
At that, Shelby finally pulled her mouth off his cock. Dan felt even smaller as his massive penis came into view for the first time. It was thick and throbbing, at least 9 inches long.
"Yes master," she said before taking his cock into her mouth again, stroking the shaft with both hands as well. Her expression was still neutral, but her blank demeanor now held an undercurrent of arousal.
