A lot of the questions in this meme assumes that you have more than one fandom - "fandom" in the sense of "IP that you consume or create non-main content for". I guess I have a couple, but pretty much my answer has to be Doctor Who and that's just really boring, isn't it? I never created content before DW, and while I did buy merchandise for and have discussions with my husband about other shows/books, it wasn't on any regular basis.
I suppose one thing I must consider is computer games. If you play a computer game regularly, that counts as a fandom, doesn't it? In a way, playing the game is equivalent to creating the story, and if you follow the game's lore, even more so. If that's true, then I must include StarCraft II. We've been playing that since it came out in 2010, mostly doing co-op multiplayer about twice a week but sometimes it's every night for months. I admit that while I've played through the original campaign, I have not played the expansion packs, but I do know the backstories of the co-op commanders.
That's an eleven-year fandom so far for me, but the one that's more dear to my heart is Asheron's Call. It's one of the "big three" MMORPGs that started the genre - the other two being Ultima Online and Everquest. We played it devotedly from launch in 1999 until 2013, when the devs decided to redesign the entire skill system. That killed the game for me because, after fourteen years of playing, it would have taken months to re-equip our characters in the new skill system to get them back to the level they were playing at.
We loved game itself - it had unique character mechanics and a fantastic loot and quest system - but we also loved the lore. We still occasionally debate Dericostian politics, regale each other with the quiet heroics of Candeth Martine, and mock Elysa Strathelar for letting her lover die at the hands of the Olthoi Queen when she had the arrow with the special poison that would have killed the queen in one shot. (Seriously. It was in the opening movie for the game. Why would the Aluvians choose that waste of space to be their queen?)
Interestingly, as I think about it, we stopped playing in 2013, which meant we suddenly had hours every night with nothing to do. And one night, my husband was so bored, he picked up a DVD he'd had no interest in ever watching and popped it in, and a minute later, I was captivated by a man in a leather jacket grabbing the hand of a blonde shop girl and whispering, "Run!"