She should have said,
“I’m not your “darling,” asshole.

He wouldn't try to sugarcoat what he was doing.
This is a textbook sample of the way such terms are used in aggressive ways every day.

That’s why he does it.

There will be a happy day..

Just a little more every day.

and passive-aggressive posturing. Like "bless your heart."

'my dear wife' or 'the wife' - it's meant as a demeaning insult.

a final "dig".

It was condescending. She was there as a professional. He used an inappropriate term for the occasion. It's a term for people who know each other well in a personal context.