Summary: Five moments where Lexie and Mark redefined their relationship. Takes place during season five.

Definitions

"So, what are we doing exactly?" Lexie Grey asked, as she was snuggled against Mark's body. Their bodies were still sticky from sweat and their legs were tangled up with each another's after they spent the last several hours having sex. After Lexie's fifth orgasm they decided they needed to take a breather, and eat, they needed to rehydrate.

"We are resting after having sex for the past three hours." Mark told her as his lips traced her jaw line. His fingers intertwined with hers, "And we are waiting for room service so we will have the energy to start again." His smirk hid his self doubt of the question she just asked.

"You know that's not what I meant." She turned herself, so she was facing him. "I mean what we are doing. We've been having sex for weeks know." She paused, biting down on her bottom lip nervously. "I guess I'm just curious on what you say we are."

"I'm not big on definitions." Mark admitted, "Whenever I try to define something is when it gets all fucked up and someone gets hurt. I don't want to stop what we are doing…I just…"

"Well fuck buddies seems kind of crude, so why don't we call ourselves friends with benefits?" Lexie asked. She surprised herself. She normally didn't just have sex with a guy, but she loved the time she spent with Mark. She loved the way she felt when Mark kissed her, the way he felt inside of her, and she just liked being with him.

"Hmm…so just because my best friend is dating your sister you think that makes us friends?" He joked. He kissed her neck; to be sure she knew he was joking.

Lexie rolled her eyes, "Fine we will just be benefits then."

Mark laughed, "Benefits it is then." He slid on top of her, kissing her on the lips. "Do you think we can squeeze one more orgasm in before room service?"

She lifted an eyebrow, smiling against his kiss. "The way you are making me feel tonight, I think we can do that." She snaked around him, so she was on top of him, "But this time I get to be on top."

"Are you still getting done at four?" Lexie asked Mark quietly as she wrote down some final notes on a patient's chart; she was out of her scrubs in her street clothes, ready to leave the hospital. She looked up to see Mark nodding, "You still want me to come over tonight?"

"Actually, no." Before Lexie had a chance to try not to look upset Mark quickly continued, "I saw everyone in that frat house you live in is on tonight, so no one will be home." He paused; he was not sure why he was so nervous. "I thought that maybe I could pick you up about six and we could go out to dinner, some place nice, and then go to a movie." He asked as they walked to the elevator, Mark pushed the down button.

Lexie broke out into a smile that she was sure stretched across her entire face as they stepped onto the elevator. "Dr. Sloan…Are you asking me out on a date?"

He smirked, "I guess I am."

"Okay, I would love to go on a date with you." The doors opened and she began to leave the elevator, but paused at the doors, "By the way, Mark…I never have sex on the first date."

Lexie had been stroking his hair for a while now, and he felt like he was going to fall asleep. "Are you going to go out with that guy?" Mark asked before he could fall asleep and lose the nerve to ask.

"What? What guy?" Lexie asked, unsure what he was talking about. For a moment she stopped stroking his hair.

"Patrick. The patient you had with Torres earlier today." Mark asked, he didn't look her in the eyes. "Callie told me about it. He kept flirting with you. And he asked you out. You told him you would think about it."

"I was just being polite Mark." Lexie told him, "I have or had no intention in actually going out with him." She paused, "Is that why you asked me to the on call room? You were jealous?" She teased.

"Have you been sleeping with anyone else, since you know, us?"

"No." Lexie quickly answered. "Have you?"

"No." Mark told her. He paused, "I don't want. And I don't want you to either."

Lexie nodded, smiling, "Okay, I won't have sex with anyone else. Just you."

Mark closed his eyes while Lexie continued to stroke his hair, "Good. Then we will just have sex with each other."

"I brought us pizza, beer, and condoms." Lexie announced as she let herself in his hotel room, "Which one should we eat/drink/use first?" She asked, setting the pizza box, beer, and condom box down on the couch.

"You have got to be the best girlfriend ever." Mark hugged her from behind before reaching for the condom box, making his decision.

Lexie didn't even try to hide her smile at the mention of the word girlfriend.

"I am so exhausted." Lexie told him as she began to take off her clothes and put on a shirt of his, that she wore for pajamas.

"I don't blame you. You had a rough last couple of days. And you spent the last two nights between Meredith and your Dad. You couldn't have got more the six hours of sleep all together."

"I'm sorry about the other day." Lexie apologized as she crawled into bed.

"Sorry about what?" Mark slid into the bed next to her.

"About springing the whole I'm going to donate a piece of my liver without discussing it with you. I mean, I would have done it no matter what you would have said, if I could have." She started to ramble. "I just should not have sprung it on you like I did."

"You are amazing." Mark kissed her, "You are an amazing daughter." He kissed her again. "You are an amazing sister." Another kiss. "You are an amazing girlfriend." Another kiss.

Lexie smiled, gladly returning his kiss, "You aren't so bad yourself."

"I love you." Mark blurted out.

"You…You love me?" Lexie was so happy it sounded like her voice was smiling. "I love you to." She kissed him. "I love you to." She smiled against his lips. "I want to have sex with you so damn bad right now…But I am so fucking tired."She frowned, "I'm so sorry, I just don't think I have it in me to do it right now."

"It's alright." Mark moved Lexie's body closer to his, "There is always tomorrow." He kissed her lips softly, "Go to sleep Lexie."

"Good night Mark." Lexie closed her eyes, "I love you."