“Not all,” Clark confessed, and the coldness inside him seemed grow.
I think "seemed to grow" would flow better.
Jonathan took a sip of his coffee, and then said, “You thought she’d never forgive you for proposing before telling her you’re Superman.”
I'm not sure she has.
He glanced over at Martha and they exchanged a smile, which Clark interpreted as they always knew she would.
It feels like there should be something between "as" and "they", such as "that", or "to mean".
He looked at her skeptically. “Only if her mother turns up alive and well, and completely alcohol-free.”
As long as Mrs. Lane is alive, I think Lois will forgive him.
Martha leaned towards him. “You still haven’t told her?”
Technically he did, just not in a way she believed him.
