Let's see...
Final Fantasy XI for like 8 years (Endgame)
I tried Everquest, Rohan and Rappelz but I barely last a month.
I currently play/rotate between
Aion&TERA 2-3 years (50 ish)
Final Fantasy XIV Pretty much since NA launch 2 years ish (Endgame)
Most of the time I play until I complete the current content or get bored to play another mmorpg/game and then come back when it looks appealing to me
I hope to play B&S for at least a year but if not taking a break to play FFXIV or Aion then come back and so on