In Tangerine by Edward Bloor how did Paul respond to Erik's violence toward Tino?

Paul is horrified when Erik strikes Tino across the face, but he is paralyzed. He doesn’t know how to stand up to his brother, who looks into his eyes for a moment in a very strange way. Paul thinks he sees fear—or maybe even sorrow. Erik walks away, leaving Paul and Tino on the ground. Tino is bleeding. He doesn’t want any help from Paul. Paul glances up and sees something move on the balcony—like a white shirt. He wonders if his dad saw what happened. Paul’s friends leave upset. Wayne picks them up. Paul is left alone, wondering what he could’ve done differently.