Because He's Brave, Indestructible, Generous, and More

"Cas, how did this happen?" Asked Dean.
"How did what happen?" Countered Cas.
"Well…us."
"You need to be a bit more specific than that, Dean."

Dean was sort of embarrassed. He was never one for those "chick flick" moments, and he knew he was going to get one for asking his ... question.

"I mean," Dean hesitated, "how did we happen? How did a fallen angel, and a guy who barely has two cents to his name come to be?"

Dean glanced at Cas's face and immediately regretted starting this conversation. All Dean saw was shock, and some surprise on his partner's face.

"Dean," started Cas, "that is a question that I will probably never be able to answer. There is no right or wrong. It's impossible. What brought this on anyway?"

"I just - I'm confused. I mean, why do you even bother to stick around? I-I-I'm a mess. My mom's dead, my father was never around. Something bad happens to everyone that I'm around. My dad and mom, Bobby, and Sammy, and that's only naming a few. Aren't you even a little bit afraid that something might happen to you too?"

Only one of them looked incredulous, and it wasn't Dean.

"Dean, there is nothing that can change my love for you. Actually, since you want to know why I 'stick around' then I will gladly tell you," Replied Cas.

"No, Cas just forget I said anything," begged Dean, knowing that a sappy moment was coming to nail him right in the face.

Cas completely ignored him.

"Dean, there's so much I could say right now, so I will. When I got you out of Hell and you jumped on the first case that you saw, and kept working case after case, that showed me that you were persistent and brave, and ready to take on the world."

"Cas, seriously - don't," Dean tried, but was again, ignored.

"Later, I knew that we had the potential to be friends when you told me that I was like a brother to you. I felt like part of the family then. And when I betrayed you, Sam, and Bobby, I was ashamed of myself, but part of me wanted you to forgive me, and tell me that it was okay. Whenever we completed a case, it showed me that no matter what you went through to kill the ghost, hunt the demon, or whatever other monster, that you were indestructible. And what you do for your family," Cas started getting teary eyed, "there are no words to explain how nurturing and generous and protective you are. There's so much more that I could say. But I thing you get the point," Cas said looking at Dean who was getting emotional himself.

"There's no reason why I wouldn't stick around, Dean. In fact, I am perfectly happy right here in this stingy motel room with you. You're the one that I want to be with. I love you, Dean. And I will always stick around."

"I love you too, Cas," replied Dean.

And those five words were all it took for Cas to know that Dean understood all that he just said, and he really did mean it when he told him that he loved him back; even if Dean did break his own rule about chick flick moments.