It's clear in the news video that Amber Robertson, Amiah's mother, has a black eye, which I'm guessing is the result of the fight that Amber and her ex had on Friday. So Amber reports the baby missing the next day, Saturday. As others have commented, the ex-boyfriend is in jail, but his arrest doesn't appear to have anything to do with the altercation between Amber and her ex-boyfriend or the fact that Amiah is missing.
Instead, he was arrested two days ago, 3/17, for criminal recklessness and leaving the scene of an accident.
So the mom asked her ex-boyfriend to drop her baby off at the sitter's house? That seems odd. Maybe Amber didn't have a car and asked the ex-boyfriend to drop the baby off at the sitter's house as a prelude to their date? As we know, the sitter said Amiah was not dropped off. I don't know whether the sitter was expecting her to be dropped off.
Watching the video, Amber is unsteady on her feet, rocking back and forth and her eyelids seem heavy. She seems to be on some kind of substance. Maybe she was given a sedative for anxiety?