Jon Snow fascinates Susan from the moment he steps onto the dock in the harbor at Cair Paravel, come to Narnia at his brother's request, to seek an ally in a war across the sea, and she takes him to her bed, because she's never wanted — never needed — someone in this way before, so instantly, so desperately, so all-consuming.

On the night before his planned departure, while they lay twined together, Jon holding her as if he never intends to let go, Susan whispers to him, "You know, you don't have to go back — "

The shock is plain on his face as he tries to interrupt her, but she shushes him and continues, " — alone. You don't have to go back alone."

(I'm sorry, it had to be the title :D)