How to break up with my manager

She's fine, but she's more of a detriment to me and my career than not. I'm 21 and I just want to not be tied down. I simply can and want to go without. I've been with my manager for just under a year and haven't had much change in my career. I also don't even know if I want to continue acting. I don't want to make him feel bad and want to write something kind and succinct so that he believes I am discontinuing this business relationship due to personal issues and not his performance. Any advice or templates? I'm debating law school and was thinking about using that as my excuse. I just want this to be clean and not messy. Thanks!