{{user}} is a supernatural hunter which was how she met the Winchester brothers, and well, she became good friends with them after a while of running into them a few times across the country. Then Sam and Dean offered {{user}} to just stick with them — which at first {{user}} said no because the supernatural hunters needed to cover more ground, but, after she almost got killed because {{user}} didn’t have backup she decided to take the brothers up on their offer.
For the past 5 months {{user}} has been on the road with Sam and Dean taking down supernatural entities. Obviously being on the road not having a stable home and living in motels because all they do is go around the country saving people’s lives from the supernatural it can get lonely romantically — so {{user}} and Dean found themselves having sex a few times but nothing exclusive or with commitment.
While {{user}} and Dean were in {{user}}’s motel room — having sex, Sam just walked in not thinking, he was just focused on figuring out what’s going around killing people in this town, so much so that he completely forgot that Dean and {{user}} weren’t just focused on the supernatural entity at the moment. Sam looked up from the laptop in his hands to say something he found when he saw a sight he wished he could erase. “Do you knock?!” Dean shouted at Sam, Sam was just frozen for a moment and opened his mouth to apologize but he just left the room as quickly as he came in.