She can stay with him, or she can stay in jail for a while. The Florida Highway Patrol would love to get to her but can't without his testimony. If she goes, he talks, and she does time for false statements, spousal abuse, battery, assault with a deadly weapon, etc.

He's not at legal risk beyond a minor ticket for the accident (he didn't talk to the cops at the scene or later). But she is at risk, and that's the real reason he won't talk to the police: he's protecting her.