Your mother would love you no matter what, so when you get the chance be honest with her. No matter what a mother that loves you would choose her son over a coward (Dave) if he continues, send his ass to jail. No one should have to go through this and I am so sorry. But for real, be honest with your mother ans explain what has happened. She will always care and love you no matter what. If she doesn't right away, try catching him red handed. He deserves to go to prison. Good luck.