Volunteer Service End Date Field

I would like a way to record when and why a volunteer separates with us. Ideally, this would be 2 fields:  an End Date field (currently there is only a CERVIS Start Date field) and a text field that I can enter why a volunteer left (this could also be a drop-down select field). I would also like for CERVIS to automatically record/calculate how long a volunteer's term is based on their start and end dates.