Dear Professor Dumbledore,
I wanted to let you know that I have bought a cottage in Hogsmeade, well Mandy and I have, and that I will be leaving Hogwarts tonight. I wanted to thank you for allowing me to stay there for the time that I did, and to assure you that my change of residence won't affect my work attendance.
Mandy and I would like to talk to you at your earliest convenience - we would like your permission to be married at the school, and maybe see if we could get you to officiate.
Thanks again, and don't worry, I'm not leaving a mess behind me.