Thanks for the advice. I guess I just don't want to think about quitting. First, I really do enjoy my work except for these conflicts, for example when he's working on something separate from me. Second, I worry about quitting so soon because I was at my previous job for only two years and this one for six months. I don't want to be seen as a "job hopper."
back your self up with well written code, committed into a VCS with proper comments. For each one that is rewritten mark those commits somewhere in a list of notes. Discuss each one with him if his check in comment is not clear as to why. When he's right, leave it, when he's being a jerk note it. If all else fails you have documented your reasons. Then go and find a new gig cuz you've done all you can.
