This is info from another article.
"I just wanted to find Amanda and give her a hug," Lee said, though she found no one at the house. She said the family had appeared happy, though Trevor Branscum recently lost a construction job and had to take another at $5 less per hour in Modesto. That caused Trimble to seek a job, something Branscum never wanted, she said.
My theory is she had plans with her friends that night. She went to the store to get a few things alone. This guy follows her there and starts an argument. The store clerk says he showed up a short time later and she came in alone. It was probably about him being at home with kids for the night while she goes out and has a good time. She tells him to stuff it and get lost. She wanted some free time for a night to herself. He jumps in her car and later the store owner sees him go out the window of the vehicle. She heads home and head outs. He probably pulls this sort of thing all the time so she thought nothing of it.
There's a big red flag. Given what came later, I'd say that Branscumbag was a tyrant who lost all control once his wife showed signs of independence.