The phrase 'became sad' is correct and usable in written English.
It is typically used to describe a change in emotion. For example, "When he heard the news, he became sad."
They then became sad and left".
I became sad, like her characters, and like them I got sadder.
Once more, an opportunity turned into a burden, and Laura became sad and frustrated.
"The police wanted him as an informant," she told the newspaper, "and he became sad and more and more introverted.
If you give back the Falkland Islands, which belong to us, you will get my vote.' They then became sad and left..
He became sadder and angrier.
As Jane's body continued to reject repeated attempts to absorb enteral feedings, I watched the medical team became sadder and more frustrated with each intervention.
His and the family's lives became sadder still when Nuland's beloved Momma died when Nuland was just 11.
Participants used increasingly concrete action identifications as they became sadder and less happy, but this effect was moderated by depression status.
Similarly, when 'surrounded' by music that presents an appearance of sadness, one might become sad, but not sad about the music, or anything else (Radford 1991).
