In The Round House, why doesn't Joe share the information he has about his mother's attacker with the people who love him?

Joe lets his friends and family in on a great deal concerning his emotional life. But there are limits; he won't share everything with them. The transition to adulthood is hard enough for Joe to deal with as it is, but in the wake of his mother's rape it's even harder. Like many young people of his age Joe's going through a whole range of complex emotions he simply doesn't understand.
He also doesn't fully understand the adult world with its many different shades of gray. Somewhat naively, Joe's always believed in a rigid code of morality, in which questions of right and wrong are cut and dried. But as he delves deeper into the sordid details of his mother's case, he realizes that's just not how things work in the real world.
What's all the more painful for him is that his father, a tribal judge, is a part of that world where the demands of justice all too often go unmet. So Joe takes it upon himself to get justice for his mother. This means pursuing his own path, an increasingly lonely path of righteousness from which his loved ones are excluded.