Twice.
I had no idea the length of time for either, so I did some quick self-research. The first one was for six months, and the second was for three years, which is funny, because if I had guessed, I would’ve said the first was probably for a year and the second was probably for a year and a half. (My chronological memory is generally pretty solid, but my temporal memory exists almost entirely as creative reconstruction.)
Neither break was because of a single reason. Really, neither was all that much of an active choice on my part. My “real” life just started getting busier and busier, and for whatever reason I felt more distant from the goings-on here, and on some miscellaneous day I just stopped logging in. Each time I came back was because I was in a lonely place in my life, although in neither case was that why I stayed. (Happily, things picked back up in one way or another in my life.) I’ve stayed because I like learning about all the different perspectives people share here—I live in somewhat of a cultural bubble, but because it’s a bubble of diversity, it’s easy for me to forget that the diversity I know through experience is only a subset of the diversity that exists in this world. Plus, I like seeing how arguments/points/opinions are presented/constructed, and there is never a shortage of those on this site!