Jaime Lannister has never been one to dream. He makes sure to be too spent to dream, whether between Cersei's thighs or out fighting. If there's no wars to be fought, he practices among the Kingsguard.
After he's lost his hand and replaced it with this ridiculous, useless, heavy gold apparatus, he's had nothing but time. Time to dream.
He dreams of Brienne of Tarth. He dreams of her standing in the bath, of her shockingly feminine body, her wide hips, small waist, perky breasts, and he wakes up panting and harder than his gold hand. He can feel his face flushed, red as if he's just finished rutting, and he's disgusted with himself. He wants to think it's because he's only thought of Cersei for so many years, but he thinks it's because Brienne is a maiden, and maidens should not be thought of such.
Sometimes he wakes with the touch of her lips on his, softer than he'd imagined because he'd only seen her mouth in a tight, stressed line.
He thinks of her often, and prays to the gods he's never believed in that she's safe, and warm.
He thinks of her leaving, of the way she looked back at him from her horse, and his heart aches and he doesn't understand. He writes it off as the ache of wanting to follow her, the want of a journey, of a purpose, but his very next thought makes that a lie.
He thinks that the true sapphires of Tarth aren't the sea reflection, but the bright blue of Brienne of Tarth's eyes.