Article continues below advertisementChris Watts' killed his whole family because of his sexual obsession with an ex-mistress, according to his pen pal.Watts, who murdered his pregnant wife, Shanann, and their two daughters, Bella and Celeste, in August 2018, told pen pal Cheryln Cadle that he couldn't get enough of his lover at the time, Nichol Kessinger."A lot of it is stuff I just won't repeat," Cheryln, 72, said to an outlet on March 8. "But his relationship with her was very sexual, very twisted, very mixed up. And that's part of why I believe he did what he did.