I repeated it for a long time. I made you sad for a long time.
I must have hurt you. Now I still cannot move.
Why is it so painful to touch you?
I think it is because I was afraid of making the same mistake and losing you.

The angel Castiel stood by and listened. Dean Winchester called for him every night, but Cas kept his distance. He watched, he did not answer. The idea of facing Dean hurt Cas deeply. He knew the hunter would be furious. And he had every right to be. But Cas did not want to say anything that would hurt him more.

Finally Cas breaks, and he visits Dean. Dean vents, and Cas listens. When Dean throws a fit, Cas has to grab him and sit him down before he hurts himself. Dean asks him why, over and over again. Cas explains, but then Dean asks why not. Why didn't Cas kill him? Cas has to think. Then he says it was because he didn't want to lose Dean again. He didn't want to repeat his mistakes.

I tried to recover the unforgettable days to stay close to each other.
You hold my hand without asking anything.

Cas does as much for Dean as he could possibly think of to make amends. Chores around wherever they're staying. Helping with groceries. With hunts. Anything. Dean never asked him to, but he never said anything against it.

Even if you don't love me tomorrow, I must love you as I do now.
Even if you don't see me tomorrow, I must love you as I do now.
I will walk together, the future not promised
It keeps walking together, to the future in which you are…

Cas notices when Dean starts letting him back in. At first, he would look at Cas. Then he would smile slightly when the angel didn't understand something. Then he laughed. Finally, after weeks, Dean treated Cas like his friend again. His best friend. Cas knows what he did was unforgivable, yet he held on to his love for Dean, and Dean came around in the end. It makes Cas happier than anything in the world.

I love you so much that I forget any suffering.
My heart feels pain every time I count the days we cannot meet.

When Metatron tears out his grace, Cas can only think of reuniting with Dean. It takes time to find him, though. Cas is not used to being unable to pop in and out of places. He is lost, and Dean could be thousands of miles away. The thought of never finding him terrifies Castiel.

The loneliness is piling up. Please don't cry alone.
Even if we are so far away, we can believe each other.

It's been weeks since the Fall. Cas hasn't found Dean, yet. A feeling is building up inside of him. It's something he's felt before; when he had first began to doubt in the existence of God. But this time it's worse. So much worse. One night he finally breaks down. He's alone, huddled on the side of a road, and suddenly tears begin to pour down his face. He can't stop them. He wonders if Dean is looking for him. He might think Cas was dead. Dean didn't know that Metatron had taken his grace. Then again, Dean had to have seen the other angels fall. Surely he would assume Cas had met the same fate, and would be searching for him. Cas just had to believe. If he couldn't believe in God, he could believe in Dean Winchester. That was something he had decided long ago.

I wish to smile as it is. I don't want you to hurt yourself.
I don't want to repeat such feelings, which have kept fading each time.
Even if you don't love me tomorrow, I must love you as I do now.
Even if you don't see me tomorrow, I must love you as I do now.

Cas never loses faith in Dean. He makes his way to every place he knows the brothers to have lived. Bobby's, Rufus' cabin, the ship where Kevin had been stashed. Finally, the Library. Every place is empty. Cas had picked the library on purpose, as it had been the most recent place. When he arrives, no one is there, but there are signs of residence that give Cas hope. Hope that he will see his hunter again. Cas stays there, at the Library, and waits to see if anyone returns to it. He isn't there more than a day before he hears the door open, and Dean's familiar footsteps echo in the chamber.

Please, only look at me. Please, don't let our hands separate.

Dean sees Cas, and they stare at each other for over a minute. Cas gets lost in Dean's green eyes. A feeling he can only describe as pure joy is rushing through his core, and it causes Cas to cry. When the first tear falls, Dean rushes at him and wraps him in the tightest hug he can muster. Cas holds him tighter. Then Dean starts crying, too. Dean Winchester is crying because his angel is safe.

I will walk together, the future not promised
It keeps walking together, to the future in which you are

From then on, they are inseparable. They spend every waking and every non-waking moment together. One goes no where without the other. It is an unspoken rule, an instinct that clicked into place the very second they saw each other. Cas helps hunt, he helps with groceries, and Dean even teaches him how to cook. Cas is a quick learner, and cooking becomes one of his favourite pastimes. Dean never stops calling Cas his angel, and after the first few times, Cas doesn't protest. Dean says it wouldn't make sense to call him his human, and eventually Cas begins to understand why. Pet names. He thinks and thinks, and eventually, he ends up calling Dean as his human. Dean laughs when Cas says it the first time, but then he pulls him close and tries to hug him to death. In that moment, Castiel realizes something. It doesn't matter to Dean that he's no longer an angel. Dean loves him anyway. And Castiel has always loved him back, and always will.