I understand how you feel. It's tough a decision to leave a job you care for and for the most part enjoy. I worked for our local school and still miss the kids...you grow to love working with them. But sometimes it is just necessary to move on with your career, especially if your current one is not getting you where you want to be.
Maybe you could still fill in on an occasional Sat. for a trainer that can't be there. You might feel better keeping in touch just a little.
The mixed emotions will fade as you begin another chapter in your life though.
Good luck!