Dr. Mark Sloan unlocked the front door of his Manhattan home. He dropped his keys at the front door like he always did and removed his leather coat and went to hang it up on the antique coat rack, but he stopped. Hanging there was a smaller mans leather jacket, one he knew too well. The house had been dark, as if no one was home, but his wife's coat was also hanging there. He dropped his coat on the floor and slowly he walked up the stairs of his New York apartment. He paused on the top level, outside his bedroom door. He took a deep breath and prepared himself for the worst. He reached for the door handle, slowly he turned it, and then flung the door open. There in the middle of his bed was his wife and best friend, naked, panting starring right at him. Mark was torn, part of him wanted to close the door and walk away, but the primal male side wanted to rip the two of them a part and beat the shit of Derek Shepherd. The two sides compromised, he stood there calmly. "I think you should get your clothes and leave Derek, Addison I'll be in my study waiting for you." He closed the door. He stood there shaking for a second then slowly made his way downstairs to his study, where he poured himself a very large scotch.

Derek Shepherd put his clothes on, Addison Montgomery-Sloan just sat there on the bed, not saying anything. "Addi," he finally said.

"No Derek, just go, don't say anything, just go."

"I think I love you Addi," he said taking her hands. She pulled them away, "Don't say that, I'm married, to your best friend, we should never have started this."

"But we did, there must be something there."

"Derek I'm married to your best friend, you should just go."

Derek didn't know what else to say, he opened the door of the bedroom and made his way downstairs. He paused for a moment at Mark's study door. He wanted to go in and explain, but what do you say to your best friend after he finds you in bed with his wife. Derek did what he was told he grabbed his jacket and left.

Addison was shaking uncontrollably when she entered Mark's study. She didn't know what her husband would do, he had never been violent with her, but she had seen him loose his temper on occasion and every time it scared her. He was sitting on his big brown leather couch, and large glass of scotch in his hands. He looked up and told her to sit. "Here," he handed her the scotch.

"You know I don't drink."

"You need it, drink it."

She did as she told and took a huge swallow of the awful tasting liquid. She coughed a bit, but continued to drink it. When she was done she handed the empty glass back to her husband. Mark stood up a refilled the glass for himself. When he was at the small bar, he turned and asked, "Was this the first time?"

"No," she said honestly.

"How long?"

"Three weeks."

Mark just nodded, three weeks, how had he not noticed his wife sleeping with another man for three weeks. He turned back and looked at his lovely wife. She was the most beautiful woman he had ever seen, and the smartest. He had fallen in love with her the first moment he saw her in Gross Anatomy, but so had Derek Shepherd. Derek had told Mark he was going to ask her out, but Mark had stopped Derek, saying that he wanted to. They had fought at first about who was going to ask her out, but in the end Derek gave in and let Mark have a shot. Mark had never thought that there was a chance that Derek had been carrying a torch for Addison for all these years. It almost didn't seem possible. Derek had even been engaged, and he was devastated when she had ended it last year, claiming he was to involved with his work. Derek was the workaholic, the one that you had to almost beg to come to parties and put work aside. He was a brilliant Nero Surgeon, but Mark was an even more brilliant Plastic Surgeon, and Addi, well she was the best in her field, NeoNatal. Out of the three of them, Derek was the one that drove himself too hard, like he was trying to prove something. Derek hadn't grown up with the perks that Mark and Addison had. Derek came from a hard working family from Queens. His mom had been a nurse and his father was a Mechanic. He was always trying to put that behind him. He was like a man possessed with trying to be the best.

"Do you love him?"

Addison turned her head quickly to stare at her husband, "No, god no, I love you...I don't what started it."

"Was it revenge?"

"I forgave you for that Mark."

Addison didn't know why she started sleeping with Derek, maybe because she was depressed, she just didn't know why it started. Maybe part of herself hadn't completely forgave Mark for having an affair on her two years before, but it really hadn't gone through her mind until he had just mentioned it. She had no clue her husband was having an affair. It wasn't even an affair, he was away at a conference and had a one night stand with one of the waitresses. When he had gotten home he had confessed all, he had cried, which was the only time Addison had seen her husband cry. It had been unnerving for Addison to see such a big strong man break down and cry and beg for forgiveness. They had moved on, neither one ever talking about it again, almost like it never happened. There marriage had almost seemed stronger after that. Then three months ago Addison had asked Mark about starting a family. She was 36 years old, she wanted a baby. She delivered them everyday, but it wasn't the same as having your own. Mark told her he didn't want children, he wanted to spend their lives with just the two of them. Addison had tried to change his mind, but nothing had worked. Addison had gone into a deep depression. Mark had seem not to notice, being engrossed with work, friends, and his other past times. It was Derek that had noticed her mood, not her husband. She had spilled her heart out to him, and before she knew it they were back at his apartment having sex. It hadn't happen all that much, half a dozen times including tonight.

Why Addi, why then?"

He started to pace the room. "I don't know Mark."

"He was my best friend!" His voice had gotten louder, not yelling, but very close. Addison could see the adrenaline start to pump and he was getting angrier.

"I know, I'm sorry."

"You're sorry. That makes it all better? I've lost someone I loved like a brother. Tell me now if I've lost my wife too." He drank his drink fast. "Have I Addison? Have I lost my wife?" He was now yelling.

"No," she said barely above a whisper.

"What? I can't hear you."

"No Mark, No I love you!"

He threw his glass across the room and it smashed against the floor. Addison jumped and the sudden act of violence. Her large green eyes looked at her husband. She wasn't scared for herself, but she was suddenly very afraid for Derek. "I'm going out!"

"Where are you going?"

"Does it matter?"

"Yes. Don't hurt him Mark, blame me, not him."

"Don't worry baby I know where to lay the blame. I'll sleep in the spare room tonight, and tomorrow go to the Pottery Barn or wherever and buy a new bed, I want that one out of this apartment by the time I get home."

Mark grabbed Addison by the shoulders and nearly lifted her up. He kissed her hard, almost brutal, but it was a kiss. He let her go and stormed out of the apartment.