No idea about who left whom and for what reason, but Karen and Kevin were still on good terms the year he won with Stacey.
You can even hear Karen saying "Well done! You did it!" when she went over to give him a hug at the end of the show.
It must be so awful for her right now, dealing with the breakdown of her marriage amd exposure of her personal life, and trying to do her job as a Strictly pro.