Disclaimer: I don't own Gossip Girl if I did Chuck and Blair would have a normal relationship. I also don't own the song unfaithful. That belongs to Rihanna.

The first time it happened Blair told herself never again. And she was determined to make it that way. Because how could she do this to Nate? How could she betray him like the last two years meant nothing to her? So she tried to stay away from him. The man that could ruin her fairytale. But something inside of her kept her going back to him. This wasn't the first time something like this had happened. It was the story of her life. She kept trying to do the right thing but for some reason she always ended up doing the wrong thing. At first it was just sex, and then she got to know him and became addicted to him. Something about the way they were together seemed to fit. But Blair couldn't bring herself to break up with Nate. They had been together forever. They were meant to be. She was suppose to get Anne Archibald's ring one day. And she couldn't bring herself to crush that dream for her mother, Nate, or his parents. What would they say when she told them that she couldn't be with Nate anymore because she was in love with his best friend. That was another thing, it was Chuck Bass. Womanizer extrondinare and Nate's best friend. How could she look Nate in the eyes and tell him that she loved Chuck. It would break his heart. Not only would she lose Nate, but Chuck would lose his best friend. Blair couldn't do that so she did the only other thing that made sense. She lied.

When Nate went out of town on business and asked her to come along, she said that she couldn't because of a project at work. That was the first lie. And it just kept going from there. He believed her at first, but after lying to him for six months he caught on. She had told him that she would meet him at Serena and Dan's engagement party because she had something to finish up at work. She met up with Chuck instead. On her way to the party she got a call from her secretary saying that Nate had called looking for her about half an hour ago. She wasn't at her desk so one of the new girls answered and told him that Blair had already left for the day. When he kissed her hello it wasn't the same. And then when she went to find Serena, the blond informed her friend that she needed to fix her lipstick. Once those words fell from Serena's lips Blair knew that it was only a matter of time before Nate confronted her. He didn't.

They barley spoke two words to each other all night and when they did speak Nate told her that he wasn't ready to get married right now. Then he asked her if it would be alright if they waited a year or so before becoming engaged. Blair said that was ok. As the months went on Blair continued to lie to Nate. Chuck was becoming a different person. He was changing and everybody thought it was for the better. They even said so at Serena's wedding. One day a year after she started lying to Nate, Blair realized how much she hated hurting him. How he died a little each time she came home late from work and he knew that she wasn't working. When they didn't make plans for dinner because he knew that she would be going out with Him. The only thing that Nate didn't know was who she was seeing. And if Blair had anything to say about it he never would. She was preparing for a night with Chuck when Nate came over to surprise her. As he watched her get ready for what she told him was a night out with the girls, Nate realized that part of the reason he didn't confront her was because he wanted to see how long it would take for her to get this guy out of her system. As she kissed his cheek to say goodbye Nate realized how much Blair had changed since she started being unfaithful. She seemed lighter, happier. It should have killed him knowing that his girl was happy with someone else. And it did when he first found out, but then he realized how easier it was to be around a happy Blair then a semi-happy Blair. He knew that eventually they would have to end it but right now they were both perfectly content pretending.

That night Chuck told Blair that he loved her. That he wanted her to end things with Nate and be with him completely. That he didn't care anymore if he lost Nate or not. She told him that she loved him too but she wasn't ready to talk to Nate yet. Give me two weeks. She said. And then we will tell him together. Chuck agreed to give her that but very reluctantly. It was during the next week that Nate found himself at the Palace Hotel one afternoon after work. He was going to go see what Chuck was doing but before he could cross the street, he heard the sounds of Blair laughing. He was surprised when he looked for the source of the sound expecting to find his girlfriend walking with one of her friends or a strange man he never met. What he didn't expect to find was her laughing like a school girl and flirting with his best friend. At one point Nate made eye contact with Chuck and the two came to an unspoken agreement. He walked away from the couple without Blair every having seen him.

When she got home that night he asked her if she was going out again. When she told him that she was in for the night he kissed her on the cheek and said he had to meet a friend. After leaving her Nate walked the ten blocks to the Palace from their apartment. When he knocked on Chuck's door he opened it without words. Chuck waited for Nate to start the conversation, knowing that he shouldn't defend himself until he knew how mad his friend really was. The blond paced back and forth for a while trying to figure out what to say to the man in front of him. He knew that Chuck expected him to be angry; hell if this had happened in high school then Nate probably would have hit him. But this was different, they weren't in high school anymore and Nate had known for months that Blair was seeing someone else. He just didn't expect it to be Chuck Bass.

"You know of all the people I imagined her seeing behind my back the last person I thought it would be was you. But it all makes sense now. You have become this different person and so has she. It happened about the same time and I just didn't realize it. I mean I knew she was seeing someone and I thought she just needed to have one last fling before we got engaged. Then I realized that this wasn't just some fling and maybe it started out that way but it has become something more serious than that. She loves you. Sometimes after she gets a phone call or text message she will start singing to herself and she just seems so happy. I should hit you. I should be mad at both of you, but I'm not. I can see how you both feel about each other and I can't be mad at that. I will step out of the way and let you two be together. It might take some time but someday I know that I will be ok with the two of you." Chuck just stared at his best friend. He had imagined many ways that Nate finding out would go down and this particular one never entered his mind.

"Thank you Nate. You have no idea how much this means to me and what it will mean to Blair." The two shook hands and parted ways.

The next night at the Palace Hotel's annual ball Nate arrived with Blair. The moments that they spent getting ready and driving to ball were cherished by Nate. He knew that he would be arriving with Blair Waldorf on his arm but she would end the evening with the man she loved, Chuck Bass. The Palace was beautifully decorated as always and everybody looked great. When Nate and Blair arrived at the table with all of their friends Chuck stood to greet them. He shook Nate's hand and gave him a nod of thanks once again. He then took Blair's hand, kissed it and pulled out her chair for her. Serena looked at Chuck weird when he kissed Blair's hand. He never did that. She knew Chuck had changed but he didn't change that much. And Blair just let him do it. Like she was use to it. Like he did it all the time. Serena knew that Blair was having an affair but she never asked her friend about it. She figured if she didn't ask then she wouldn't have to feel bad when Nate found out. Once again Serena eyed her best friend and her step-brother. They were sitting next to each other now? And was that Chuck's hand on the back of her chair? Nate usually did that. What was going on here? Serena turned to her husband and silently asked him what he thought about it. In typical Dan fashion he shrugged his shoulders. Blair noticed her friend thinking about something and wanted to know what it was.

"S is there something wrong?" the blond in question looked at her friend in surprise when she spoke to her.

"As a matter of fact there is B. I was just wondering if there was something going on between the three of you that the group should know about." Serena responded to her friend motioning to the three people she was referring to. Blair was about to respond when Nate jumped in.

"Actually Serena, Blair and I have been drifting for some time now and I thought that it was time that the pretending ended." Blair looked at Nate like she didn't know what he was talking about. When she opened her mouth to question him he stopped her.

"Blair, I know about it. I've known for some time and at first I thought it was something you needed to get out of your system but I know different now. You are happy Blair. Happy in a way you never were with me. At first it hurt but then I realized that we were both fooling ourselves into thinking that we were right for each other. I was ok with it when I didn't know who it was, but when I saw the two of you yesterday I didn't know if I could be. Then I saw how happy you were, how happy he was. I had never in my life seen either one of you that happy. I'm not completely ok with this yet, but I will be. You two belong together. So I have to be." Nobody knew what to say after Nate's little speech. Dan looked lost as usual. Serena looked shocked and little confused. Blair looked relieved. And Chuck looked ecstatic.

"So wait a minute. What did I miss? Nate are you saying that you not only knew Blair was seeing someone else but you are ok with it? And who is the other guy?" Serena asked him. Nate nodded yes to the fact that he knew and was ok with it. Serena was about to ask Blair who the guy was once again, when she noticed the look on her step-brother's face, and the arm around Blair's chair.

"Oh. My. God! You and Chuck? Blair really? Of all the guys I thought you could be seeing he was the last one on my list. Who would have thought that you and Chuck would hook up? I sure as hell didn't." Blair just looked at her friend and smiled.

"You know S I said the same thing when you got together with Humphrey over there. He is the last guy I would have ever pictured you with. But when you asked me to give it a chance I did, because something drew you to him. Something made you look at him twice. Something made you want to get to know him. And in the process of getting to know him you fell for him. Right?" Serena nodded in response.

"That is kind of what happened with Chuck. Remember about a year ago when I got into that huge fight with Nate. Well I went looking for something to do because I had to get out of the house. Somehow I ended up at Victrola and in the arms of Chuck. I told myself it would never happen again because I couldn't do that to Nate but something kept pulling me back to him. Before I knew it I was seeing him on a regular basis and lying to my boyfriend. I got to know a different side of Chuck, one that I had never seen before. The one that explained how Nate and him were such good friends despite being so different. I hated what I was doing to Nate, but I couldn't make myself give Chuck up. I knew I was going to have to break it off with one of them eventually and I think my heart decided a while ago that it would be Nate to get hurt. And for that I am truly sorry Nate. When we first got together you were the boy of my dreams, but we all have to grow up sometime and I didn't realize that when it was my turn I would be falling out of love with you. I do still love you, just not in the way we both fooled ourselves into thinking I did. I am so glad that you are taking this gracefully. I hope that we can get back to being friends again one day because you are one of my best friends and I would hate to lose you. I promise that until you are one hundred percent ok with this that Chuck and I will try not to rub it in your face." Nate smiled at her and gave her a hug.

Chuck and Blair took that as a sign of appreciation. The couple gave sigh of relief that telling their friends was out of the way. The group chatted happily all throughout dinner and when people started getting up to dance Chuck got up and asked Blair to dance. The rest of the evening was spent on the dance floor in each other's arms. Serena and Dan even shared happy news that they were going to be parents. Even Nate found a nice girl to spend the evening with. Her name was Rebecca and she loved to dance. As the group of friends thought of how their lives turned out they all smiled when they realized that they got their happy endings.

Wow! This was some story. I'm not even sure I like it. I like some parts of it, but then other parts feel like they just go on forever. I don't think I write Chuck and Blair very well. I think Nate is a little easier. Please give me some feedback. I would love to know what ya'll think of this. This story is slightly AU and is based off of Unfaithful by Rihanna. I heard that song the other day and immediately thought of this. I have some other oneshots that I am thinking of posting possible in the same universe but if nobody likes the first two than I won't post the others. My other Chuck/Blair story is called He can't live without her. I hope you enjoyed this!

Brianna