Ok So I Am In High School And I Went

Ok so I am in high school and I went on my dad's ipad and found some interesting things.... He has a secret email, and that he has been on a website called cheating housewife like multiple times... And I know FOR SURE that they weren't ads, and so I confronted him about it and asked why he had an account on it, and he started stuttering and lied to my face and said he had no idea what I was talking about... What do I do now? Do I tell my mom?