Dear Mr./Ms. Bossname,
It is with sadness and regret that I must resign my volunteer position.
During my time with the nonprofit, I have worked passionately to support its mission and serve our clients well. However, the day-to-day stresses and emotional nature of the issues faced by the community we serve have come to a head, and I can no longer continue without sacrificing my personal well-being. I am simply burned out.
I am sorry for any inconvenience this may cause. I would like the opportunity to say goodbye to my current clients. Also, I would be happy to continue to serve the cause intermittently, such as at community events or the annual fundraiser.