It bears remembering that there is a strong implication that Candy does not truly care for Allan, but rather for what their affair represents to her. She feels particularly cheated not out of jealousy for his marriage to Betty, but because his fidelity signifies the end of her own infidelity, which had increasingly become a defining aspect of her identity. This is a deeply Christian community in late-70s Texas, where marriage and family are paramount, second only to God. In her liaisons with Allan, Candy existed outside the social norms, free from the constraints of nuclear family conservatism. However, Allan's rejection of her - a rejection she confesses to Sherry she is struggling to come to terms with - confines her once again to the sexless prison of traditional family values.

This, one suspects, is the reason for Candy's rapid and complete unraveling. Love & Death does not do a good job of emphasizing the passage of time, so her reaction seems irrationally severe. It helps to view Candy's sudden spiral as a profound existential terror. But blimey, she makes it obvious. When Allan tells her that Betty has found a lump in her breast that two doctors have deemed benign, Candy insists on dropping by. She can fake concern and interest for as long as it takes Allan to pull into the driveway. As soon as he does, her eye-rolls and discomfort are so evident that it's no surprise when Betty looks out the window at them and immediately realizes that something is going on between them.
It may seem like I'm overanalyzing things, but I'm validated by a scene later in which Candy asks Pat to attend Marriage Encounter. In their conversation, she asks him outright why he thinks he's there, as if on Earth, and he gives a perfectly serviceable answer - to plant roots and grow fruit and spread seeds, like a tree. When he throws the same question back at Candy, she has no answer. She doesn't know. Don says something similar later to Pastor Ron, who is sulking about none of his parishioners liking him. He claims people just want to raise their kids, love their families, and love God. But what if they don't?
Candy tries to mask her existential angst by replicating Allan and Betty's path through Marriage Encounter, naively believing that if she can fix her marriage, she can get over the rejection. But Candy and Pat evidently do not believe in the retreat - Pat describes it as a cult - in the same way Allan and Betty do. It sort of works, in its own way, but it's a temporary measure; a Band-Aid over an open wound that needs a stitch before it festers.
It transpires that the wound has no real time to fester. Following the Marriage Encounter, Candy and Pat attempt to fake happiness, but he stumbles upon one of Allan's love notes to Candy. Pat rushes to Sherry for confirmation that the affair is over, not questioning its validity - a crucial moment of self-awareness. When she confirms the affair is over, she heedlessly tips Candy off, contrary to Pat's instructions. Nevertheless, Candy waits for Pat to bring up the issue, which he does in a self-loathing letter, acknowledging his failure to keep Candy satisfied, leading her to commit adultery.
Does Candy feel shame, as she claims? I believe she might. Regardless, Olsen does an extraordinary job of conveying it. After these revelations, everyone settles into a strained domestic routine. Candy and Pat try to carry on as normal, while Allan and Betty are somewhat detached; they're over in Wylie, not Collin County, and Betty's disputes with Pastor Ron keep them away from the church.
However, Alisa is friendly with Candy's daughter and is always at her house. It's while running an errand for her that Candy ends up visiting Betty at home. Allan has left on a work trip, and Betty is frazzled again - she was advised to stop taking birth control in response to the benign mass, and she thinks she might be pregnant again.
The moment Candy arrives at the Gore house, there's an instant sense of foreboding, as it's recognizable from the cold open of the premiere. The yellow laundry basket is on the couch, the playmat and rocking horse are on the floor. It's no surprise when Betty confronts Candy about the affair. The episode ends with Candy confessing, Betty nipping outside, and returning with the wood-splitting axe that will eventually kill her dangling by her side. But we don't see the murder - we leave things on the promise that it's coming. With five episodes still remaining, it'll be intriguing to see how much more of this story there is to tell.