I think the optimal way to maintain a relationship is to keep communicating no matter what your mood might be. I've lost many friends during my prolonged depressive episodes because I suddenly cut off contact due to isolation. When I bounce back, I often avoid restoring contact due to embarrassment. Despite the fact that I know my pattern, it's difficult for me to change it. If nothing else, the fact you don't have face-to-face contact with this person might make it easier to maintain somewhat regular contact via email. Good luck!