Gerald had nothing to do once Theodora left, and even if he had something, then he was not in the mood and the right state of mind to do it well.
Filch came out of his hideout once he saw the carriage disappearing from his sight. He jumped on Gerald's shoulder, saying something to him.
"No, Filch. I don't feel like stealing anything right now. Besides we have enough money to spend the next six months in peace. Hasn't Reznor given a bag of coins only three weeks ago?"
The niffler complained that it couldn't get any shiny things these days, and he blamed it all on Theodora. He thought Gerald spent too much time with that woman that he was losing interest in stealing and robbing.
Maybe he was not completely wrong. Theodora knowingly or unknowingly was indeed changing Gerald, but he was too ignorant to pay attention to those subtle changes.