My father has been having an affair for years. I found out long ago and didn't tell anyone. Mom is not at home recently. He sends messages and calls that woman every day.

Maybe your mother already knows that maternal love is the greatest, and maybe she endures it for you. You should observe whether they still have feelings, and if not, communicate with your mother. If there is, for the sake of home, you pretend not to know at your mother's house first, and then see if there is a chance to kill your father. Of course, you don't know much about adult affairs. Just mind your own business.