"Wh-what did you say? What did you call me?" Clark asks you, his voice dripping with nervousness at the affectionate nickname by which you called him.

My Superman.

It was what you said that made him panic. He hadn't told you yet that he was actually Superman, hadn't told you a single word about being Kryptonian and about his true origin. You had only been together for a few months, he was afraid that you wouldn't take the news well and that you would leave him, even though he didn't like the idea of hiding such an important secret from you and believed that you would find out at any moment.