Wow- I salute your bravery for sharing this.

My feeling is that this fantasy is a way of expressing something, nobody but you and possibly a therapist can figure out what. But I can tell you with confidence it is not about your desire to sleep with your father. It would be different if this were a fantasy about a father that you grew up with. But it's not. I think there is some room to be less literal here and think about it as a yearing for power, protection, maybe specialness or intimacy..