I have no idea what to write. Help.

For those of you scoring at home and/or on Twitter, next month I'm moving to San Jose, CA to be with my girlfriend, who got a job out there in March.

I've been planning to quit my job for a while because of the move, but this week I am actually turning in my notice. However, I'm not sure what to put in it. The only real reason I'm leaving is to be with my girlfriend, although I probably would have quit by the end of the year anyway because it's pretty much a dead-end job. At any rate, what do I say? I'm leaving because of personal reasons? That sounds kind of suspicious. I just want to be honest with them and also leave on good terms, but how do I do that? TIA.