A/N This is based off of Season 7, episode 1. We'll wait, Cas... we'll wait.
Dean Winchester was sitting somewhere familiar.
A lake.
No, that wasn't exactly specific, but Dean knew it because it was Dean's lake. A lake where he had been fishing, had been handed a note, had noticed he was-
"Dean?" Dean looked around to see who the questioning voice belonged to.
"Cas? What are you doing here?" Castiel, his guardian angel, was standing next to him with his standard look of confusion and his trademark tilted head. But if Cas was here, then Dean must have been-
"I heard where you were and thought you might want company," Dean smiled up at him genuinely, "You are OK with company, aren't you, Dean?"
Dean scoffed, shaking his head and looking back at the lake where his fishing rod was slightly bobbing along with the water. "I'd love your company, Cas. I'm not as heartless as they say I am." Cas just continued looking confused, but proceeded to sit down on the edge of the pier alongside Dean's chair. They both sat there in silent content, until Dean looked over and saw that Cas's shoes were dangling above the water. "You know you can take your shoes off and put your feet in the water, right? I promise it won't bite." Dean smiled fondly at the angel as he slipped off his shoes and resting his feet in the cool water, ever so slightly splashing around. He was almost like a timid little kid, and it only made Dean chuckle. Laying aside his fishing pole, he got up from his chair to sit next to Castiel. All of a sudden, a small yelp came from Cas's lips as a fish nipped at his toes. He gripped Dean's arm tight in fear, making Dean bark like a dog. "Dude, it's not going to hurt you." Castiel turned to Dean, his eyes wide in fear. Dean looked sympathetically at him, placing his hand on Cas's shoulder.
"I promise I won't let anything happen to you."
Castiel smiled, raising his foot out of the water, wiggling his toes around to make sure they weren't broken. Dean took this moment to splash some water at Cas. The look of alarm was enough to make Dean start laughing again.
"Why did you hit me with the water, Dean?" Cas almost looked hurt, and it made Dean feel kind of bad that he had even done it in the first place.
"It's fun. You can splash me back too," He watched as Cas stared at him, "Go ahead." With some hesitation, Cas dipped his hand into the water and hurled it at Dean's face. He got a lot in his eyes, and ended up sputtering out with a grin on his face, "Oh, you're so going down."
Dean started splashing copious amounts at Cas, who returned it with showering his own big amounts at Dean. They both started laughing, Castiel's face brightening up which only made Dean laugh even more out of pure happiness.
Dean's foot caught on the edge of the pier, catching him in surprise as he toppled over into the water, grabbing Cas's trenchcoat and sending him in along with him. They both slipped underneath the water and came up with gasps of air, Dean still holding onto Castiel's trenchcoat.
"Dean! Dean, I can't swim!" His legs fought against the water, his arms thrashing against Dean's sides.
"Yes you can! Hold onto me." Dean grabbed Cas around the waist, holding him against him as Cas wrapped his arm around Dean's neck to use him as a sort of flotation device.
After Cas's initial panic subsided, Dean started laughing so hard, he thought he was going to die.
"I told you I wouldn't let anything happen to you." He finally got out, looking into Cas's deep blue eyes that rivaled the water's blueness. Castiel continued to clutch at Dean's neck tightly, smiling brightly at him.
"I know."
Dean could feel something tugging at Cas, pulling him away from Dean. His face turned from happy to confused as Castiel's fingers started slipping from his grasp on Dean. "What... Cas?"
Castiel's face had a smile on it, as he let his hands break away from Dean. Dean cried out in horror as Cas started sinking into the dark water. "Castiel!" Dean grabbed onto his hand, holding on tightly, determined not to let his friend go. "No, Cas! You're my best friend!"
Castiel continued to smile, his chest already completely under water. "And I love you." Dean's hoarse voice pleaded as he watched his friend's fingers begin to slip from his hand.
"I know, Dean. And I love you too." With that, he let go of Dean, completely submerging under the water.
Dean cried out but nobody was left but him. He was alone.
Dean woke up, his body covered in sweat, and his face tear stricken. "Cas?" He called out, but no one answered. It was then that he remembered – he remembered the lake in his dreams and he remembered that Cas was still at the bottom of that lake where the Leviathan took him.
Getting up from his bed, he walked outside to the Impala in nothing but his boxers. Opening up the trunk, he pulled out the small bundle that was hidden in the corner. Castiel's trenchcoat. Holding it tight to his chest, Dean Winchester sank to the ground, cold, and bare, and cried. He cried because there was nothing left to do.
Dean was alone.