When you are practicing, much of what you're really doing is building muscle memory - that is, the repetitive motion conditions the muscles to do the various combinations required easily, without thought. When you're discouraged about "practicing", try thinking about building muscle memory and ease of motion. It might encourage you to keep working on your music.
To be in tune, you've got to listen to yourself with one ear and your accompaniment (guitar, band, CD) with the other. Hear both at once.