I don't feel it would be in my best interests to be in any relationship right now....just because I'm so mentally preoccupied to give my undivided attention. When we plan things, I'm sometimes half-heartedly going about things; plus, we don't really have much in common, and her personality doesn't mesh well with mine. But that's the main reason why I want to break it off, surprisingly. I'm just tired. Mentally, and physically...this is the last thing I need on my mind. Can I explain this to her without sounding like a self-centered jerk? Because I'm really not.
Why don't you say what you just did here to her. You guys are very young, this can't be totally unexpected at your age.