Thanks for posting a new question, Erika! I've been wanting to see this thread updated again, but couldn't think of anything to ask.
The longest I've worked on a story from start to finish is 46 months, or almost 4 years. By My Side and Secrets of the Heart actually both took 46 months to finish - the difference is that I worked on BMS consistently and it just ended up being 200+ chapters long, whereas Secrets is only 25 chapters long but was written very sporadically until this past summer.
When Rose and I finish Song for the Undead, that will be my new record, because we've been working on that story for over 4 years already. I have stories that have been in progress for even longer, but they are not likely to ever be finished LOL.