How do I get my dad to just stay out of it?!?

My dad had his girlfriend and her son move in last year. I sleep over Avery weekend, because I like being there. My dad's girlfriend and I get along very well, and I really like her. Her son is 15 and I am 14. Her son is just so annoying and irritating beond belief! The little devil is always trying to piss me off. I participate in a pageant at least once a month, and the little creep shows up just to be sarcastic and make me mad. He and I have kind of like a love and hate relationship. I'm not saying I hate him, because we really care about each other but he is like the devil when it comes to irritating me. Last time I brought a guy home that I really liked, he ruined it for me by embarring me. So I decided to get even and do something that I know would piss him off. He has his skating friends come over almost every day. They are actually cute, so I decided to tease them a little. It wasn't anything serious, I just wanted to piss him off. I know he doesn't like it when I am around his friends. I started talking to his best friend. I actually liked him, we've been together for about 6 months now. Even though at the beginning I just wanted to get on his nerves, I actually ended up really liking the guy. But my dad's girlfriend's son didn't take it well. Ever since that, he stopped talking to my boyfriend, and he blames me for "ruining his friendship". He still hasn't let it go, he hardly talks to me anymore. Now my dad wants me to break up with the guy because "family comes first" and he says that what I did was wrong. But I am definitely not breaking up with the guy, I really just think my dad should stay out of it. I just don't feel like arguing with my dad over it, but I am definitely not breaking up with the guy. How do I get my dad to just stay out of it?