Disclaimer: I do not own Supernatural
First and foremost, Dean was not a sappy guy. He didn't do "chick-flick-moments" and that was alright with Cas. Cas didn't get the whole "chick-flick-romance" thing Dean proclaimed to be so averse to but Dean didn't like it so Cas didn't like it. That being said, Cas and Dean went out one night for a little alone time. They found a field that Cas assured Dean would not be found by anyone else. Its flowers made a soft bed and the two had an amazing night. And no, it wasn't just sex. They had dinner under the stars too. And then they fell asleep. And because it was such a perfect night, they didn't feel weird sleeping on the bed of flowers. It was the perfect temperature, but on the scale of perfection it was verging on mildly chill. Castiel put one wing over Dean who seemed pleased by this because he rolled over in his sleep and moved closer to Cas. Sure his wings were in tatters, not many feathers left after his fall, and one was bandaged due to injury so that it was completely unusable but Dean was happy, Dean loved him, and so Cas was happy. He had Dean, and he was happy. And it may have very well been a sappy "chick-flick-moment" but that didn't mean Dean would ever tell the story as such. And Cas, not knowing better, would agree.
"Cas?" Dean mumbled as his arms held Cas firmly against him. "You know I love you right?" Dean asked.
"Yes Dean you tell me often." Castiel replied.
"But just saying it isn't enough. You know right?" Dean asked.
"Yes Dean."
"And I may not be perfect and I know I won't live forever but I love you. And that's perfect. And that will live forever." Dean said.
"Yes Dean." Castiel said smiling. The saying "so happy it's like I grew wings and flew to heaven" made sense to Cas now. Dean had never said anything like that before and Castiel loved every word.
"I love you too." Cas said.