Tell your parents. Suddenly this whole thing is no longer your problem. If they confront him and he gets angry with you for telling them they'll probably move to take you out of the equation since you aren't really the issue here. If they don't confront him it's their decision which I'm sure they'll make carefully. They're also probably in a better position than you to decide how to act on this. This is all provided you feel you can confide in your parents about this.