Dear _________,
As you may have already heard, I will be leaving _______________ on January 15, and moving to a neighboring city. It was a really hard decision for me to choose to enter a different industry, but I was given a unique opportunity to explore something that I have been passionate about for a long time. As I truly consider you to be my second family, I plan to keep in touch with each of you, and I’ll stop by the office to see you whenever I’m in the area. Thank you so much for providing a wonderful work environment that allowed me to learn and grow in so many ways.
Sincerely,
(YOUR NAME HERE)