I'm a dad with a daughter around your age. I'm sorry to say but your dad is a raging asshole. He should understand that as a young adult you are going to make mistakes and to help you, not give you a wildly disproportionate punishment.

If my daughter was in that situation (especially with a guy more than ten years older than her), I'd be wanting to protect her from the fallout, not throw her to the wolves. The fact that you don't have your mother to support you just makes it especially egregious. I'm sorry you are having to deal with this. If you feel like it is unfair - well, it actually is.