(Y/N) had been with the boys since practically the beginning. She first met Sam Winchester when he was running around hopped up on demon blood and she put him in his place. When Dean came back though, she started occasionally joining them on hunts. A few here and a few there until it became an everyday thing. She eventually became part of their small little family.
Dean really took to her, always combating her sass with his not-so-witty comebacks. He thought of her as his little sister, always looking after her even when they bickered. Sam however saw her in a much different light. Apparently it was a surprise only to the couple, when he proposed. (Y/N) had just finished hacking off the head of a vampire when Sam realized he couldn't live without her. Before he even knew what he was doing, he was pulling her to him. He rested his forehead against hers and whispered, "Marry me", and she said yes in a heartbeat.
Six months later though, things changed. One day, (Y/N) just retreated into herself. She no longer brought the energy and laughter into the room when she entered. She no longer had witty remarks towards Dean when he said something stupid. Instead of sitting around the kitchen drinking beers with the boys, Sam now found her drinking the good bourbon while secluded on the metal stairs that lead inside the bunker. She even stopped sleeping in their shared room, leaving the sheets cold on her side when Sam woke up.
Sam tried talking to her, so did Dean, but she would just brush it off to stress or insomnia. She knew she couldn't hold them off forever, so she made her decision. Sam had taken off on a supply run, leaving her and Dean alone in the bunker. (Y/N) found him sitting on the bed in his room, drinking a beer and looking over a potential case.
She gently knocked on the door frame before clearing her throat. "Ah, so she finally speaks!" Dean replied without looking up from his computer.
In a small voice (Y/N) asked, "Can I come in?" Dean simply waved his arm over an empty spot on the bed. (Y/N) crossed the room and sat down on the edge instead of curling up in the center like she used to do. "We need to talk, Dean."
"What do you think Sammy and I have been trying to do for the past month," he questioned, "talking to oursel-".
"I'm sick, Dean."
"Text Sam, he'll pick you up some tissues."
"Not that kind of sick."
That made Dean finally look up from his computer. He looked at (Y/N), really looked at her and finally saw her. Her eyes weren't as bright as they normally were, and her skin was paler. Her nails were bitten to the bed and her hair was flat and a little on the grungy side. Dean would say she looked like Hell, but with Crowley there he had dressed it up a little nicer.
"What are you talking about?" He asked, worry and concern evident in his face. (Y/N) hesitated for a moment, trying to collect her thoughts.
"Well, remember that werewolf hunt back in June were I got thrown into the brick fireplace?" (Y/N) asked. Dean nodded his head, questioning where this was going. "Well ever since then, I was getting these really bad headaches, like crippling, stabbing, crying my eyes out headaches, and I didn't want to worry you or Sam, and I normally just deal with it, but it was so bad and I knew something was wrong and -."
"(Y/N)! Spit it out!" Dean yelled, pulling from her from her rambling. (Y/N) took a deep breath to calm herself before letting it out in defeat.
"It's a tumor," She finally let out. Dean just sat there in disbelief. "It's right here," (Y/N) pointed between her right ear and temple, "in the medial section of my right temporal lobe and it's pressing against my limbic system."
Dean just stared at her, not quite sure what he was hearing, "What does that mean?"
"It means I'm going to die."
That was not an answer Dean was expecting, let alone okay with, but before he could fight her on it, he suddenly remembered his brother. "Why are you telling me this and not Sam?" She remained silent, staring at her hands and playing with her engagement ring. "(Y/N)? Why didn't you tell him?" She just looked up at him with watery eyes and Dean finally realized she wasn't going to tell him.
"(Y/N) you have to tell him," Dean pleaded, "He deserves to know what you two are up against."
"No, Dean, it's what I'm up against" (Y/N) said in a quiet voice.
Dean finally noticed the duffle bag sitting in the hall across from his open door and it hit him, "You're leaving, aren't you?" The way he said it broke both of their hearts.
"This was never the way I thought I would go out of this world," (Y/N) said, "but you two don't need to go through it with me. I'm going to keep hunting till I can't anymore and then I'm going to do what I have to do."
Dean knew immediately what she meant and he cringed at her words. "No, you're not leaving, this isn't how you go and you're going to fight this," Dean all but begged. "There are treatment options, we can figure out a way, Cas can heal you!"
"You mean the angel that has no wings?! Like that's going to work! And for treatment options, I'm not going to sit down and let myself rot. I was born a hunter and I'm going to die a hunter." There was no use, (Y/N) had made up her mind.
"Do you know what the limbic system does, Dean?" He just looked at her like a confused, injured animal. "It does a lot, but one of the major things it deals with is memory. It's going to start out as headaches, and then it's going to grow to nosebleeds as it raises my blood pressure. As it continues to grow, it's going to press up against my limbic system until it starts to cut off blood flow and the system starts to die. First I'll begin to lose my train of thought, or forget what I was supposed to be doing when I walk into a room, and eventually I'll forget my own name. I'm going to turn into a mess of a person until other parts of my brain shut down, killing off my kidneys and my liver and my lungs until I suffocate to death and then it will stop my heart. Now tell me that's something you want to be there to watch?!"
Dean now had tears streaming down his face. The girl he thought of as a sister was dying in one of the most painful ways, and there was nothing he could do. After some time, he found his voice again, "What do you want me to do?"
(Y/N) was playing with her ring again, avoiding the question. She spun it over and over and over again before suddenly stopping. Her fingers hovered over the thin metal before slowly sliding it off and handing it to Dean. "Don't tell Sam. It will be easier if he thinks I left him and he hates me." (Y/N) pulled a sealed envelope with Sam's name on it out of her back pocket as she stood up and handed it over.
Dean followed her motions and stood up to grab her and embrace her in what could quite possibly be their last embrace. He held her to his chest and they cried together until she eventually pulled away, picked up her bag, and left the bunker.
—
When Sam returned with the week's supplies, he found his brother at the kitchen table three quarters of the way done with a bottle of his favorite whiskey. "Hey, where's (Y/N)?" Sam asked, but he was only answered with a motion towards the envelope and ring that sat on the island counter top in the center of the kitchen.