What do I do? My best friend slept with my dad.

Hi.
I am Paulina, I am 25year, I was in my room sleeping when my friend came checking for me but met my dad first on her
way to my room, only for my dad to drag her to his bedroom and slept with her.
I woke up and came out from my room, sitting on the couch in the sitting room only to see her and my dad coming out of from my dad's room.

I don't know what to do right now, I am angry and confused,

What should do?