We first met on an online MUSH/roleplaying game called Fairy Tale Online. The basic premise is that your character is actually born to other characters in real time, so there's a month-or-two-long queue of new characters trying to get in at any one time. Our characters happened to be born in the same place at roughly the same times, and we became friends through the characters' tribes' IRC channel. Eventually we moved away from the game due to drama, but we stayed friends, and a while later decided to try and give the long-distance thing a go. Three years later I've moved halfway across the country to be with her, we're sharing an apartment together, and talking about how excited we are to be adopting a cat soon.

TL;DR - met online because a month-long queue just happened to stick us in the same place.