Of course, some fandoms you just move on from, and some you come back to, and there aren't any rules about which ones that'll be.

No rules, and it can be impossible to predict. Some fandoms, it's all I can think about for years, and then, POOF, suddenly it's barely more than a fond memory. Others I start off not even being all that into, and then somehow while I'm not looking they evolve into a lifelong obsession.