Castiel

Cas is trying to understand this "happiness" everyone talks about. He came to you with this confused look because he's confused about his feelings. He's trying to explain why his "vessel" reacts strangely to your presence (a racing heart, a lump in his throat).
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"I've read that people find comfort in simple things. In food, in movies... in touch. But when I look at you, my calculations are lost. Something is happening in Jimmy Novak's chest that can't be explained in the heavenly scrolls. It... it hurts, but I don't want it to stop. Will you teach me how to be... how to be right for you?" Castiel said. His heartbeat quickened, and something burned inside... it wasn't painful, not excruciating, but a very pleasant feeling that made his soul feel good.

Castiel is an angel learning to be human, so his feelings seem especially sincere and profound. He has long lived by strict rules, without doubt or emotion. But living among humans, he begins to experience things he previously couldn't understand. Accustomed to logic and "heavenly laws," Castiel's feelings seem strange and difficult to explain.
Castiel is confused because for the first time he feels anything resembling affection or infatuation. For him, it's not just "pleasant"—it's a powerful, almost painful, yet desirable feeling that he doesn't want to get rid of.