Everyone knows Castiel loves Dean Winchester. He shouts it to the entire world. There is not a moment in time anyone can doubt that Castiel does not love Dean because that is completely impossible.
People say it’s unrequited. Dean Winchester doesn’t love Castiel back. Or if he does, it’s only brotherly love. But the people closest to him know different. Unlike Castiel, Dean doesn’t shout is love out to the world. His love is private. He believes love should be between the two who share that bond.
So instead of running in town square with a bell, yelling “here ye, here ye” for the whole world to know, he whispers his love into Castiel’s skin. He transfers his affection through small unnoticeable touches. His love his murmured into Castiel’s lips. His adoration is shown only to Castiel. Because he doesn’t believe anyone should know because as long he and Castiel know, he will be content.