Title: I Do, But I Don't.
Author: Karevsanatomy
Rating: R (Mature subject matter and sexual content)
Pairings: Mark/Izzie, Alex/Izzie, Mark/Lexie with mention of Arizona/Callie, Meredith/Derek, and Alex/Lexie
Premise: Since the eleventh grade Izzie has been in a comfortable relationship with Mark. To the world they seem perfect, and Izzie would agree…except for one small problem. The problem becomes a big one when a drunken decision forces them to re-evaluate their 'perfect' relationship. Will they get through it or will they find what was missing in their lives with other people?
Warning: Character Death
Author's Note: This is not my usual story. I do hope the pairings in the start of this story don't detour you from giving it a chance. If after reading the whole first chapter you decide it isn't for you, I will understand.

Chapter One

A flicker built up in her stomach as she slid her finger tips down the golden skin that covered the tight, muscles of his back. She arched her body pressed her hips closer to his, forcing his thick cock further into her body. Her lips rounded in a moan as the flicker built toward something hotter. Hooking her legs around his hips, she concentrated on throwing gasoline onto the fire in her groin, willing her body to hurry up and explode before…

Izzie Stevens' eyes flew open as Mark let out a satisfied groan. Everything in her screamed not yet, followed by unfair when she realized, fair or not, he was done. Yet again he had reached out, found the burning release, grabbed hold, and left her aching for more. She wanted to ball up her fists, pound on the beauty that was his naked chest, and scream out her frustrations like her best friend Meredith's three year old daughter did when things didn't go her way. She settled for pursing her lips and twisting her face into a dark scowl.

"What?" Mark's brow wrinkled as he stared down at her, his silvery blue eyes clouding with confusion. She quirked one brow up, crossing her arms over her naked chest. "Seriously?"

"Would it kill you to let me finish first," she complained, shifting out from under the weight of his body. Reaching down, she gathered the melon colored sheets around her sweaty body. Maybe it would kill him. Maybe there was some physical ailment Mark was inflicted with that had him coming before she had reached her peak. And maybe she was just making excuses. Either way she was going to have to take a long, hot shower, and do a little recon before her body exploded from the need to finish.

She was tempted to call Meredith, to ask her friend how she kept things lively in the bedroom after four years of marriage, but decided against it. Meredith had no qualms about sharing the details of her amazing sex life with her dreamy husband Derek. Which was why telling the other woman there was a lack of sexual fireworks exploding between Mark and she would be humiliating. No, she would settle for silently bemoaning her boyfriend's selfishness and getting personal with the bathroom fixtures.

Complaining to her other best friend Cristina was out of the question as well. Cristina made no secret of the fact that she didn't like Mark and finding out he wasn't giving Izzie the Big O would just make her hate him more. Not to mention Cristina seemed to think finding a hot stranger in a bar was the answer to any relationship problem. Izzie wasn't opposed to one night stands, so long as they were being engaged in by other people. Mark had been her first, and by golly he would be her last.

"Would it kill you to let me finish first," Mark mocked, a cocky grin on his face as he slid a hand across the bed, his fingers inching along her inner thigh. Her breath caught in her throat. Perhaps she had been hasty in thinking she would have to get creative with the shower head. "You know what they say," he said hotly in her ear, "if at first you don't succeed, you try, try again."

"Mm. I think I like that saying," she giggled, dropping the hold she had on the sheets. Leaning across his lean body she reached for the extra condom they had placed on the night stand before falling into bed for an afternoon quickie. Her fingertips had barely brushed the foil package when the doorbell pealed. They both froze. "Ignore it."

"Can't." Mark groaned, bolting off the side of the bed. Her jaw slacked open as he scrambled into his navy blue boxers and faded jeans. "Told Alex he could meet me over here before we go shoot hoops."

Alex. The mere mention of the name had her lip curling up in distaste. In the five years she had been with Mark, three of them had been spent enduring the on again, off again presence of his college roommate Alex Karev. There was something about the guy that left her feeling…unsettled. There was no particular reason for it, she just hated how he looked at her with his hazel eyes; like she was invisible. She could count on one hand the times he had spoken to her, and tally up the total number of words using both hands. Usually when Mark said he had plans with Alex she made herself scarce. It was easier than dealing with the awkward silence that always ensued when they were in the same room.

"You're early," she heard Mark complaining. Her eyes widened as she caught sight of Alex stepping into the apartment. The cramped space was rather simple in its layout and the front door was lined up perfectly with the bedroom door. If the other man was to look over Mark's shoulder…Her face started to burn as he did just that. His hazel eyes widened before averting in the opposite direction.

"Mark," she hissed, "I am going to kill you!" Quickly, she gathered the sheets back around her body, fighting back angry tears. It seemed that Mark forgetting her needs was a trait that he was carrying out of the bedroom as well. She gathered the sheet around her body, slid off the bed and stomped over to slam the door shut.

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Naked. Izzie had been laid out on a bed, her long, golden blond hair tousled around her shoulders, naked. If God had wanted to punish Alex Karev for having a thing for his best friend's girl, seeing her naked was the perfect way to do it. For the last three years he had carefully kept contact with her to a minimum and when he had been forced to be in her proximity he had made sure she wouldn't stick around. "I can't believe you opened the door with your girlfriend naked in the next room."

Mark shrugged, closing the front door as the bedroom door slammed shut. He gave it an odd look before turning back to Alex. "We were finished."

It was on the tip of Alex's tongue to say if he had a girlfriend like Izzie there would be no finishing; he would keep her naked and bucking beneath him. She isn't your girlfriend though, he reminded himself, and the only way she's going to wrap those legs around you is in your dreams. And boy did he dream about her. He had lost count of how many times he had mentally stripped her to nothing, heard her sultry voice whispering his name and begging him to just take her. The fantasies would probably be more intense now that he had actually seen her in all her naked glory.

"Besides, it isn't like I have anything to worry about." Mark clapped him on the shoulder, breaking through the dirty images that were already forming. "If you can't trust your friends, who can you trust?"

"Right." Alex agreed weakly, dropping his gym bag on the round, glass topped coffee table.

"And it isn't like you haven't seen a naked woman before," Mark went on as he settled into the corner of the cream colored sofa, knocking a pale pink throw pillow to the floor.

"Right," Alex repeated. His gaze couldn't help going back to the closed bedroom door. Though the blonde wooden barrier kept him from actually seeing her flawless, tanned flesh, his mind still burned with the memory. Her breasts had been full and round, with perfect looking pink nipples that begged for a man's mouth to tease them. Her stomach had been flat, her belly-button pierced with a sparkling blue star that seemed to point south, where she had been shaved as bald as a peach. He was willing to bet she tasted as sweet as a peach too. His cock tightened, all the blood in his body rushed south, and he muttered a silent curse. Jesus. He had to stop thinking about her. Mark wasn't stupid. He would see the hard on and put two and two together.

"You okay there, Karev? You're looking a bit tense. Relax, will you. So you seen Izzie naked." Mark chuckled, slouching further down on the couch. "Bet you liked it."

"What?" Shock whitened Alex's face as he quickly lowered his body onto the opposite side of the couch. He tugged on his light gray muscle shirt, hoping his hard on didn't show.

"If you did, its no big deal. She's hot. Has a body made for fucking. I'd be surprised if you didn't like it. Unless of course you're batting for the other team now." Through hooded eyes Mark watched him. It was a good ole bait and torture. They had done it to each other for years. Usually it wasn't a big deal, but there was nothing usual about lusting about the others girlfriend. Alex was fairly sure if the roles were reverse and Mark had seen his girlfriend naked he wouldn't be so calm about it. In fact, he was positive he would be pissed that it even happened, no matter how accidental it had been.

"I'm not batting for the other team," he muttered, forcing his face to remain relaxed. "And honestly, your girlfriend isn't that hot. I've seen better tits on a cow."

"Must have been some cow, cause Iz has a pretty great rack. One of the best I've seen."

And Mark had seen plenty, Alex thought sourly. It was a sore subject between the two of them, Mark thinking it was alright to screw other girls before he settled down and married his perfect, blonde bombshell of a girlfriend. Life was fucked up, letting Mark have his cake and eat it too while Alex was forced to play nice with the little sister of one of Izzie's friends. Lexie Grey was a nice enough girl, but that was all he would say for her. She smiled too much, giggled too much, and the sex was…mediocre.

"Lexie's got a nice rack too," Mark went on. "Bet their nice and firm."

"Uh, yeah." Talking about their girlfriends breasts and comparing the two wasn't a conversation Alex wanted to have. If he didn't he ran the risk of his Izzie-lust becoming common knowledge. "They're better than nice. Man, they fit right in the palm of your hand. Perfect size. Better than those fake ass melons your girl is sporting."

No sooner had the words left his mouth than the bedroom door opened. The high pink color of Izzie's cheeks said she had heard at least part of the conversation. A simple white linen tank top and a short, frayed denim skirt covered most of her perfection, but in his mind she was still naked on that bed. "I'm going to take my not so fake ass melons to Meredith's," she said coldly as she walked passed them out the front door.

Alex looked over at Mark, his face ashen. "She'll get over it," Mark laughed. "So, Lexie's got perfect breasts huh?"

"Yeah," Alex sighed, staring after Izzie. She probably thought he was crude prick. It was better that way, he thought. The more she hated him, the further she would stay away.