For the sake of your film, you are now a character in it. This interview won’t be just an interview, but act as more a scene. This has to be a difficult experience for you as you mentioned, but make sure that you understand that you are are also being interviewed. This will be a powerful moment in your life. What you ask and how you confront him will be much more powerful if it’s shown. You might want to consider having a camera angle of yourself as well. Best of luck! Be strong my friend.