In my case, in the last ten years I've been subscribed to the game a grand total of 58 months, of which:
8 months were spent playing BC (started playing back in november 2007)
18 months were spent playing WotLK (had a nice guild, was committed to raiding, really loved the expansion but had to take long breaks due to IRL demands)
5 months were wasted playing Cataclysm (guild fell apart, people I knew started to unsub, I became mostly a solo player and absolutely hated what they had done to the game)
15 months were spent playing MoP (was still a solo player, I unsubbed during the first couple of months because of the heavy focus on dailies and reps but had a blast pugging flex/normal/hc and getting the legendary cloak with all my toons during the last patch of the expansion)
8 months were spent playing WoD (I shouldn't have kept the subscription running for that long tbh, but the legendary ring took a long time to get. The last 2 months were almost exclusively spent leveling an army of alts through invasions)
4 months have been spent playing Legion (for a solo player like me it's been a pretty meh expansion so far, with few redeeming qualities. I hope it gets better in the next 6 months or so, for I'm planning to return when the second-to-last wing of Antorus LFR opens)
According to Wowpedia each expansion has lasted roughly 2 years:
• Burning Crusade: 22 months (2007-01-16 – 2008-11-13)
• Wrath of the Lich King: 25 months (2008-11-13 – 2010-12-07)
• Cataclysm: 22 months (2010-12-07 – 2012-09-25)
• Mists of Pandaria: 25 months (2012-09-25 – 2014-11-13)
• Warlords of Draenor: 21 months (2014-11-13 – 2016-08-30)
• Legion: 12 months (2016-08-30 – still counting)
So what's your story?