Personally, I don't believe that KB was planning to go to dinner with PF at all. What she told her mother is another story. And I don't think PF was stressed because it is nearly impossible to fit in time with someone on the side on the day of a major holiday like Thanksgiving. How would you explain disappearing for an hour or two during that day? Unless KB was killed shortly after arriving home from Safeway and KK was still not yet in town I don't see how it could work. I could see it if KK had family in the immediate area that she was visiting for the holiday but she doesn't have family anywhere near the area (despite people who have the same common last name) and a time period of being unavailable would not be noticed. But if you traveled over 14 hours to spend a holiday with someone I can't imagine that you would not be perplexed, confused, hurt, or even angered if they were to disappear for whatever hours would be necessary to do what PF is alleged to do. If they both lived in much closer proximity I could see how it would be possible to play both women. But not with the great distance, especially in time, to have KK come to CO or PF to go to ID I don't see how it could work for any length of time without it blowing up in his face.
Of course, I have believed for a long time that the relationship between PF and KB was long over and their only interaction concerned exchange of their child.