Disclaimer: I do not own the characters, nor do I pretend to, this is all just for entertainment and I am not making any money on this story. The song used is Somebody That I Used To Know by Gotye.

A/N: Some crazy thoughts run through a mind when you find it impossible to sleep. I had asked a friend for a prompt and this is what I received. I'm not exactly sure how to describe this story, but I would really like to hear what everyone thinks about it. Pezberry is not my OTP, but I have recently started shipping it and while Rachel is one of my most favourite characters to write I'm not exactly an expert on writing Santana. I hope you enjoy the story.

Prompt: Rachel finds out that Santana has cheated on her with Brittany.

Now and then I think of when we were together, like when you said you felt so happy you could die. Told myself that you were right for me but felt so lonely in your company, but that was love and it's an ache I still remember.

The rustle of a sheet, a pleasure moan, someone else's name on her lips, these are the sounds that haunt her. Every night she awakens, looking over to the girl sleeping peacefully beside her, but all she can see is her thrashing with someone else in their bed, her hands touching someone else's body, someone else touching her body. Rachel Berry was faithful, she had devoted everything she was to the girl sleeping beside her, she loved her like she had never loved another human being, but the same couldn't be said for Santana Lopez. With her knees pulled up to her chest, the sheets falling low on Santana's naked form, images from the previous week flashed through her mind.

-Flashback-

Rachel had arrived home to their apartment early to surprise her girlfriend. Things between the two girls had been rough recently and Rachel wanted to do something special for Santana. She had skipped her last class of the day and made a detour to the grocery store picking up supplies for a romantic dinner for two to be followed by a relaxing bath and the night ending with Rachel showing Santana how much she loved her, but she never expected Santana to have a surprise of her own.

Stopping in the kitchen, Rachel put away the groceries and went about prepping everything for later. She knew that Santana was out, they both had classes as well as jobs, but when Rachel heard the creaks coming from their bedroom she lost all train of thought. Her overdramatic self automatically assumed that a burglar had infiltrated their apartment and found his way into their bedroom, for all she knew he could be rifling through their underwear drawer sniffing their panties as she stood there head of lettuce and a jar of tomato sauce in hand. Quickly coming to her wits she placed the items down and replaced them with a butcher knife, if Rachel Berry was going down, she vowed to do it fighting.

Carefully she made her way to their bedroom, the door was slightly ajar and Rachel could see movement in the dimmed lighting of the room. Pushing the door open and peeking her head in Rachel's attention was drawn to the rocking of the bed, the sounds of Santana panting, of her moaning, it wasn't until Rachel noticed the movement under the blanket did she realize that her girlfriend wasn't alone and that someone was under the covers doing things to Santana that only Rachel should have been doing. And when Santana finally reached her peak, moaning out "Brittany" was when the knife dropped, clashing to the floor and startling the occupants of the bed. Santana stared at the disturbance, her gaze slowly lifting to see that of her shocked girlfriend.

"Rachel, I can explain," but Rachel had heard enough. She had caught her girlfriend, the one person in the world who was supposed to care about her, love her, and be faithful to her, with someone else's head between her legs. Rachel thought that she could have dealt with it if it had been a stranger, if Santana had just brought some random home and fucked them in their bed, but it wasn't someone that she didn't know, in fact it was someone she knew very well, someone she considered to be a friend. Rachel had never imagined to think of Brittany Pierce as competition. After high school had ended and everyone had gone their separate ways Rachel and Santana had found each other. Santana and Brittany had amicably split, deciding friendship had been best for them and Rachel had finally realized that she didn't need Finn in her life to survive, she could do it well enough on her own. Both girls were in need of accommodation and with their newfound friendship decided to room together, neither one of them expecting to fall in love.

Rachel had run out of their apartment and straight to the only place she could think of, she found herself being consoled by Quinn Fabray, the blonde that she never thought would befriend her was now the one taking care of her and as Rachel explained the situation to the girl she couldn't help but think that Quinn was right when she said that Brittany and Santana had something that no one else could match, that the two of them, no matter what happened, were for some reason meant to be together. As much as she agreed with Quinn, she didn't want to believe it. She had spent a week at Quinn's dorm, doing her best to avoid the fiery Latina and trying to decide her best course of action, but when Santana showed up at Yale, begging for Rachel to come back home and promising that it was a onetime occurrence that would never happen again, Rachel believed her and now, here she was…

-End flashback-

A moan emitted from the body lying next to her and Santana rolled over, her chest now exposed and she shivered covering herself up with the sheet. Rachel sighed as she stood up from the bed, not exactly sure what to do with herself. She hadn't been able to get a full nights rest since moving back into the apartment, she felt weak going back to Santana, but love made you do crazy things and Rachel knew that she had done crazier. The tiny brunette was still hurting and as she slowly pulled on a pair of sweats and grabbed her iPod she chanced a look at that clock noting the red numbers flashing 5am before she walked out and went for a jog. It was the best way for her to clear her mind and she knew that it would help her decide what needed to be done.

Coming to the one conclusion she didn't want, Rachel made her way back to the apartment, walking up the stairs and quietly entering their home. She turned around after locking the door and coming face to face with a half-naked Santana staring at her. "Where have you been?" She could tell be the girl's tone that she was upset and a glance at the clock had told her that she was gone for a lot longer than she had anticipated, what was supposed to be a twenty minute jog had turned into a two hour run and Rachel gulped as she made her way to the kitchen to grab a water bottle with the Latina behind her. "I asked you a question, Rachel. Where the fuck have you been?"

Turning around she sent a glare at the other girl. "And exactly who are you to question my whereabouts with that tone? I went for a run, Santana, in case you haven't noticed I haven't been able to sleep in our bed since finding Brittany between your legs, or have you conveniently suppressed that from your memory because I know that I haven't!" No matter how many times she had tried to forget, tried to replace the images with her and Santana, nothing would work. "How many times do I have to explain it to you, Rachel? It was an accident." The brunette scoffed at the taller girl, walking into the living room and taking a seat on the chair. "So, let me understand this correctly, you accidentally fell into our bed, naked might I add, and Brittany managed to do the same with her face accidently landing between your legs? It's all coming together now, Santana. Or did you accidentally mistake your blonde ex-girlfriend for your current brunette one, because I can see how that's a simple mistake."

Rachel watched as Santana closed her eyes, rubbing her temples as she slowly made her way to the couch. "We talked about this. I thought you had forgiven me." Rachel had almost lost her resolve as she stared at the other girl, looking into her eyes and almost seeing the Santana she fell in love with, but all she could do was shake her head and laugh. "I tried, I really did, but when I close my eyes and all I can see is her head between your legs and you moaning out her name, I ask myself why am I even trying? You've never sounded like that with me, San. I've never been able to please you the way she did that day and every time you touch me now or every time I touch you I won't be able to stop wondering if it's her you want instead. I can't do this. I thought I could, but I can't. I love you, I truly do, but I can't stay here knowing you love someone more."

Rachel could feel the tears begin to stream down her face and had to stand up to avoid allowing Santana to console her. "I'm moving into the guest bedroom for now, until I can find another place to live. I don't want to hurt like this anymore and if I stay with you, no matter how much I love you, all I'll be doing is hurting. I'm sorry." She didn't wait for a response, instead Rachel went to what was once their bedroom and began moving her things out of it. It wasn't that she didn't love Santana, Rachel always would, but she needed to let the girl go. She needed Santana to finally be free and find the happiness that it seemed she was keeping from herself and Rachel needed to do the same. The one thing that Rachel regretted was being unable to maintain a friendship with the other girl, it hurt too much to see her with Brittany knowing that if she could have just gotten over it that would have been her, it should have been her, but it's easier to move on without a constant reminder and as much as she would always love Santana, Rachel found herself someone who would always love her and with each passing day her love for Santana began to fade and Rachel found herself living the life she always wanted.