Author's Note: This is set in the 6th season, right after Mark and Lexie broke up. The italicized lyrics and title are from Dave Matthews Band's song Stay or Leave.

Summary: What if Mark followed Lexie to Mer's house after they broke up, looking to reconcile?

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Stay or leave

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I want you not to go

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Mark knew the minute he let her walk away that it was the wrong thing to do. Sure, she didn't want Sloane as her step-daughter and she didn't want to be a step-grandmother at twenty-five. But…They could figure this out, right? It wasn't too late. It was only…What, a few hours since she'd left? They could still fix this. There was no way this was over yet.

Mark doesn't bother knocking. He knows the door's unlocked and he's sure someone will be awake at this hour who'll recognize him and drop the burglary bat.

"Lex," Mark calls, taking the stairs two at a time and moving past Meredith and Derek's bedroom. "Are you—" He starts to ask, looking around for her only to stop short.

"Mark." She calls his name softly, walking towards him. She's forgotten about everything that's happened since they broke up just a few hours ago. It was all lost in a haze of wine, or at least that's what she'd like to think. It was nothing, she reminds herself quickly. It was just passing the time, easing the heartache. Sure he can see that. Surely he realizes—

But it wasn't that to Mark. Just as his eyes focus on his recent ex, he takes in the sight behind her: a half-naked Alex Karev. Which, usually, wouldn't be a problem, wouldn't be weird. That is, if Lexie wasn't wearing an obviously hastily put-on tank top and shorts. No bra, no shoes.

He flinches away as she moves closer. Her eyes tighten, watching him move away from her in disbelief and disgust.

"Mark, stop," she tells him, knowing his brain's jumped into overdrive, analyzing the situation before he has a chance to even process what's happened. "It's not—It's—It was nothing. Nothing." She takes another step towards him. "I promise you, it was nothing."

He stares at her silently for half a minute before closing his eyes, his face wiped clear of expression. Detached. It's his strategy for dealing with any painful experiences or emotions. "What, exactly, was nothing?" His voice is low and quiet, enunciating each word perfectly. His tone just barely remains even as he watches her face.

Her eyebrows knit together, her eyes pricking, knowing that he won't understand. He's one of the most stubborn people she's ever met. Once he makes up his mind, that's it. Over and done. No, Lexie thinks furiously. This isn't over with. Not yet.

"Mark, come on," she implores him, taking a step closer. When he steps away from her, Lexie grabs his arm, forcing him to stay where he is and listen to her. "It was a mistake, I promise," she tells him solemnly. She gives him a small, involuntary smile. "Don't you trust me?"

He stares at her for a minute, as if trying to siphon the truth out of her words, before his eyes flit to Karev's in the background. "I…I did," he murmurs half-heartedly. His eyes are still focused on Alex's. "Not anymore."

"Mark," Lexie calls as he turns away. She follows after him, but stops helplessly when he doesn't even bother to look back over his shoulder. "Mark, come on!"

"Sorry, Grey," he mutters, but it's Meredith in her bedroom doorway that he's glancing quickly at, not Lexie, before heading downstairs. "Won't happen again."

He seems to run down the stairs, he moves so quickly, and before anyone can take a step, he's out in the fresh and cold Seattle air. He breathes it in, still moving, as if there hadn't been enough oxygen within Meredith's house.

For the first time since it happened, Mark can actually understand how much what he did with Addison hurt Derek. He can feel it in the tightness of his chest, accompanied with the disorienting feel that he can't get enough air into his lungs, and the loss of balance that comes with feeling as if you're stomach's dropped out of the middle of your body.

And then it gets worse.

He realizes how much he must've hurt countless other people, just trying to relax, to get a release from the repetition of his daily life. He realizes how much his little conquests could have forever ruined or irreparably damaged so many relationships.

And he hates himself for it.

Then, it that moment, he'd give anything to be somewhere else. To be someone else.

He's jolted out of his thoughts when he hears footsteps pounding down the stairs and out into the front lawn. He doesn't stop when he hears her indignant shouts behind him. He simply continues walking forward.

"Mark, come on," Lexie yells after him, a few steps behind. When he doesn't turn around, she reaches her hand out, doing her best to wrench him backwards to face her. "Stop," she commands him. And though her strength doesn't do much to actually move him, he turns around nonetheless. He wants desperately to look anywhere but at her, but he knows that if he shifts his gaze, it will only land on Karev. And if it lands on Karev, Mark will just end up killing the son of a bitch with his bare hands, he's sure of it. So he keeps his eyes trained on her face, no matter how much it hurts.

"Can we please talk about this?"

"There's nothing to talk about," Mark replies, his shoulders slightly hunched, his voice smooth and quiet, seemingly careless. "You were right. We're over."

"Mark, you know I didn't—" Lexie begins, only to fall silent when she sees he isn't listening to her. They both know she knew what she meant when she said those words. She tries a different tactic. "It can't be because of this," she tells him. "You came all the way over here—"

"I drove six blocks," he replies dryly.

"You know what I mean." He doesn't respond, opting instead to keep his eyes trained on her face. "You came all the way here…You—you can't just leave without discussing this first."

"What's to discuss?" Mark asks, his voice oddly quiet. He's usually one to yell; if he's angry or upset, his voice gets louder and indignant. Yelling she's used to, yelling she could take. But this…This grim-faced defeat… "You slept with Karev," he states. She opens her mouth to say something, but he just plows on through. "Not even three hours after you left me, after you told me we were over, after you packed up and left, you're here, fucking someone else." A patronizing grins spreads over his face. "Fantastic."

"I was drunk," she replies hotly.

"Well, you don't seem very drunk now," Mark counters, his voice bored.

"Yes, well, you showing up out of the blue sobered me up," she defends herself.

"Right. I'm sure it did."

"Mark, it's not my fault," she tells him.

"Oh, really? It's not your fault? Somehow I doubt that," Mark replies, condescension lacing his tone. He has to make an extra effort not to glare at Karev, who he's noticed had followed them outside into the night. Meredith is standing beside him, shifting from foot to foot, unsure of what to do.

"Mark," she says, looking into his eyes. "What happened with Alex was a mistake. I didn't—" She sighs. "I was upset, okay? I was upset, and I wanted to feel better."

Mark just shakes his head, chuckling in disbelief at the irony of it all. "You know, if the situation were reversed, I'd get it." He shrugs. "I'd get it. I mean, I would expect something like this from me. You'd expect something like this from me. Everyone would. But you…" He trails off, raising his calculating eyes to appraise her. "I thought you were better than this. I thought you were different."

"You don't get to talk to me like that," she replies hoarsely, his words hurting her more than she'd care to admit.

"Don't I?" There's an edge to his question. "I wasn't the one who left you, Lex. I wasn't the one who walked away. You did that all by yourself."

"I wouldn't have had to if you'd just talked to me about Sloane."

Mark shakes his head again, looking away. "You never wanted her around."

"Mark," Lexie sighs, exasperated. "I am twenty-five. I don't want to be a step-mother to some girl you just met! I told you that."

"You could've tried to talk to her at least. Get to know her."

"Tried?" Lexie asks in disbelief. "Tried? Are you kidding me? I had to force you to say two words to her! And even then, you barely spoke to her unless it was a completely necessity."

Mark doesn't respond, opting instead to look past her, taking in the darkened neighborhood behind Meredith's house. Lexie stares at him, waiting for him to say something—anything—so that she can try to change his mind. She knows what she did was stupid, but was it really unforgiveable?

Still staring into the darkness, Mark freezes for a moment, his lips pressing together. He thinks back, his mind reeling, before speaking again. His mask of indifference is broken for a spilt-second as Lexie sees hurt and vulnerability flicker over his features. But it's gone by the time he speaks.

"Were you…Were you drunk when you came to the hotel?" He asks quietly, blood boiling.

"Mark," Lexie admonishes him, her voice wavering, her bottom lip trembling. How can he bring that up? Now? How could he question what we were in the beginning?

"What? I want to know. I really want to know," he tells her, the harshness returning to his tone as he crosses his arms, staring down at her. "Were you? Is this what happens when you drink?" Lexie just shakes her head; unlike Mark, her disbelief and anger are written all over her face.

"No, Mark, I was not drunk then. I was perfectly sober, and you know that. You made sure of it." She sighs, looking away. "I was drunk tonight. I was drunk because you picked her over me!"

"Oh, don't say that like she's another woman," Mark snaps, annoyed. "She's my daughter!"

"Right, one you've known for less than five months, who you're now ready to house and raise a infant with?"

"Lexie, don't—" Mark growls.

"No, I get it, I mean, whatever. You missed out on everything. With your family, with Addison…Hell, maybe she's got your kid now," Lexie sneers, furious.

"She doesn't," Mark replies, his voice low and harsh, almost menacing. But Lexie's too fired up now, and his warning tone doesn't stop her.

"You sure about that? Why don't you call her up and—"

"She terminated it," he cuts her off, his voice emotionless, almost dead. The yard is silent for a few minutes as everyone takes in the meaning behind those words. Lexie's eyes lock with his, trying to discern what he's feeling—but unlike his tone, his expression is unreadable. After another minute, she steps forward, raising her hand to comfort him.

"Mark…"

He steps away automatically, and his eyes finally leave her face. When he looks up, he can Meredith and Alex, frozen in shock, standing on the porch. There's another figure, just behind them, seeming to have just woken from a deep sleep. Mark meets his old friend's eyes before he turns around, and he can see the tiredness had been wiped from them with his words.

"I get it," he says softly. Lexie glances to him, confused. Get what? Why Addison aborted—

Derek meets Mark's eyes, confused as well. Mark sighs, staring right at his best friend, raising his voice. "I am sorry, Derek," he says slowly, honestly. "And I understand why you walked away."

Mark's eyes fall to meet Lexie's again, and he can tell he's hurt her. He'd like to take a sick sort of pride in this fact, but all he feels is guilt. He'd like to hurt her as bad as she hurt him…But he knows that actions speaks louder than words, and even he can't do that to her.

Lexie, Meredith, and Derek all know the meaning behind his cryptic words. Mark can tell she understands exactly what he's hinting at by the way her eyes tighten, her lips meeting in a hard line—no doubt trying to keep her emotions in check in front of him. Lexie is about to open her mouth to say something, but before she can, he turns away, and the previously hidden tears fall unchecked down her face.

She watches him go.

She watches what she thought was the best thing in her life turn around and walk away from her.

All because of one stupid, drunken mistake. That's all it took.

Just one mistake, and his beliefs in himself, in her, and in who they once were are shattered into hundreds of irreplaceable pieces.

Stay or leave

I want you not to go

But you did

She stands there for a few moments. She keeps standing there as moments turn into minutes, and the minutes never end. She can hear, one by one, the spectators retreat back into the warmth of the house, until there's only one left. She can hear the crunch of feet on gravel and grass behind her, signaling an approach.

"He didn't mean that," Derek tells her gently, coming to a stop beside her. She doesn't respond at once, just takes a shuddering breath and wipes her face for the first time. She stares straight ahead as she speaks.

"You don't know that," she whispers, her voice cracking with tears. Derek glances over to her, wishing he could do something to help her, to comfort her. But he can't think of anything. She isn't Meredith, he isn't Mark, and he has absolutely no idea what to do.

"Come on," he says instead. "Let's go inside."

Stay or leave

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I want you not to go

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But you should

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It was good as good goes

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