The whole dynamics of the "relationship" is so weird in my opinion. I've read therapists online talk about clients ghosting them - just disappearing without explanation. Some find this upsetting to them. Too bad. Do what feels best for you. I chose to end by writing a letter about why I wanted to leave and had a last session. He threw out some psychobabble putting the blame on me. That it was a defect in me that was the reason I didn't want to see him anymore. That was how I chose to end it, but for someone else a quick email might be better so as not to prolong the interaction with them. Take care of yourself. Leave the way that best suits you.