How long do you stay with one therapist?

To ensure i stay stable, I believe i will need therapy for my entire life. Even if its not as frequent as my weekly sessions right now during a tough time. Even if it’s “maintenance sessions” every month or something. but i know you’re not supposed to have the same therapist forever. so am i supposed to just have a different therapist and start over a bunch of times? How long generally do you stay with one therapist? How long is too long? Why do people say you can’t stay with one therapist for life lol