BD1 ("My feelings for you have changed") July 2011. Actually left August 23, 2011. BD2 when the OW was confirmed was November 27, 2011. He absolutely cycles with the seasons though, and will ramp up in the spring with a lot of manic behavior that peters out by the end of autumn.
It's interesting though that my mother left my dad August 4, 1994, and my dad left my stepmom on August 23, 2003 (and there's no way Hoss would have remembered that to align it). I very much believe there are not just biochemical reasons we sway with the seasons, but spiritual ones, too. It's odd to me my birthday is the Autumnal Equinox, OW's is the Summer Solstice. Coincidence, or Hoss has some serious transition issues (y'think?!?!).