How do I get my dad to understand? I just don't know what to do. There is a story with this, heads-up.?

You do not have to speak with the therapist while your dad is there that is against your privacy rights. no one can force you to speak while he is there. Matter of fact the whole reason people see a therapist is so they can get everything off their chest without worrying if someone else will find out. Unless of course your are going through family counseling which is something different and your father should be involved in that.