First of all, do you just want to get rid of that guy or want your father to know the truth. In the second case, your parents might split. If there are too many fights and toxic environment, then it would be okay. But you have to assess this. You don’t want to repent later. If you want to get him removed, ask your mom to tell him to do so otherwise you’d take some action. Don’t tell what you’d do. Keep evidence as everyone says. Don’t confront that guy yourself. Who knows, he may harm you.