Can I "break up" with my therapist over e-mail. Or do I have to do it in person at my next session? It's not acrimonious, I just can't afford it anymore. What is the protocol in this situation?

UPDATE: Thank you so much everyone for your advice. I am going to write my therapist an e-mail saying I can't continue our sessions because of my financial situation, and would like to discuss "moving forward" at our next session.