GhostofCain
Ancient Mariner
I was in a band for 3 years too. It ended with a classic Eric Cartman line: Screw you guys, I'm going home.
Really, when you are in a band for so long, you can see negative traits of every person in the band, including yours, grow. I was becoming a person I didn't want to be, so I quit.
I quit over musical differences and to preserve a good relationship with my former band mates, something that was particularly important as my brother was one of them.