Why are my parents so hard on me?!?

So, I am 17 years old and I have been dating this guy for the past 6 months. The past couple months we've been hanging out with each other everyday and have become more like bestfriends than anything. Well all of a sudden my parents are trying to tell me i can only see him one day a week, and i know they're wrong, i just dont know what to do or say to help them understand where im coming from. They have nothing to worry about, he comes from a good family (both his parents are doctors) and we have never been in trouble together. I make straight A's, I work, and I'm always respectful to my parents, I honestly think i should have more freedom then i do! My curfew on weekends is 11 and on weekdays its usually 930, and im SEVENTEEN! Ive never been in trouble, im active in school activities like cheer, dance, and volleyball, im just an all around good kid and im treated like im still 12! i need help!