Switching piano teachers?

I'm 16 years old and I play clical piano. I'm thinking about switching teachers because I don't think I'm getting very far with the teacher I have. I think he's an excellent teacher, but there's this other teacher that he is friends with that I have met before. His students are playing Chopin Etudes and Mozart Piano Concertos and I'm playing Bach Inventions and Early Beethoven Sonatas. I'm in an ok position as far as my level goes, but I really want my piano level to EXCELL. I'm my teachers top student by far, the next person below me is way below my level. That tells me that I'm the only "serious" student of my teacher. I just don't want to hurt my teachers feelings because he's been my first and only piano teacher for the past 7 years. How do I go about this?