He yearns, desperately, to be more human for her. He tries, hopelessly, to be Vulcan enough to not feel that. She asks for and expects neither. She wants him for who he is and that is overwhelming, intoxicating.
She is a cadet, he a commander. She was his student. It is less than optimal circumstances.
He looks at her and understands why the sands of Vulcan were once stained green with the blood of those who fought and died for their mates. He looks at her and understands why when humans begin to love, they call it falling.