1) The fact that you're asking this is a good sign that you need more info than your current teacher may be able to give you. It sounds like you should get together with other teachers regarding the issues you're looking to improve. When choosing another teacher, make sure they have expertise in your desired area of study. If you want to work with the bow, find an orchestra player in a good local symphony, and/or one who teaches at the HS or college level. 2) If you've decided you have had enough with your current teacher, just tell him in a nice way that you've decided to check out some other approaches and that you appreciate his help up to this point. He may be the first to recognize his weaknesses in certain areas of playing. Very few of us can do it all. If you still want to keep seeing him, do so, and arrange some lessons with others, too. You don't have to close the door unless you want to.