My latest just broke up with me when they realized I don't consider them a bestie (but they did consider me a bestie).
My longest bestie-ship: 2 years. The shortest: 1 semester.
Please define BESTIE however makes sense to you. I consider a BESTIE to be whoever I think about the most when I don't think about myself (FYI I have no biological children).
I'm being deliberately vague so I can get a wide variety of responses.
My best friends stayed the same for the last 15 years ( I'm 35). Even when I met a reasonable amount of other people by now and even when I eg. Didn't see most of them during COVID-19.
But everything stayed the same when we met again. It's more about character matching than "how often we meet" for me.