so I have this acoustic guitar that I've had since middle school. (I'm in college now). I don't know exactly when it happened but ever since sometime, the tuning started to mess up. Its not that the tuning would mess up, the sound from the lower frets are fije but when I play the higer frets like the 12th, I have to play the 11th and lift it a bit to make the 12th sound.
My question is. What's happened exactly? And also, Can this be fixed?