Normally, I’d suggest being honest and straightforward when something’s bothering you. But in this case, since he was a good client, it might be kinder to come up with a gentle excuse not to see him again, just to avoid hurting his feelings. That said, it could be tricky to pull off. Another option is to simply say you’re busy whenever he tries to book another appointment, he’ll likely get the hint and stop reaching out. If he’s persistent, then at that point, it’s best to be honest with him.