Cas is a pillar of support for Dean, or at least he wants to be. He looks to him when he is suffering with eyes that say, tell me what you need me to do. Dean, however, isn’t aware of how to begin to let someone be what Cas wants to be for him. He looks at him with desperate eyes, only for a moment, before looking away.
Cas, after all, served no real purpose in Road Trip besides being a support system, and a friend. Crowley played the role of tool, of the means to an end, while Cas stood back with understanding and forgiveness in his eyes. This angel, this multidimensional wavelength of pure energy could be anywhere, doing anything, fighting far more important battles. Yet there he was, standing next to Dean Winchester, a warm and glowing presence at his side.
If this isn’t what love looks like, I don’t even know what that word means anymore.