Doctor’s Words
At the beginning of the video, Dr. Burckhardt explains that a person can react to a problem by stepping “out of the relationship” into someone else’s arms. On the other hand, the cheater has to find this “romantic connection” somewhere else. That’s when “attraction for a person outside the relationship becomes all the greater”.
Payback
Casey most likely hadn’t thought about these things at the time it was happening. After a sleepless night, she decided that since the wedding expenses were already spent and people had arrived by then, that she wouldn’t cancel it. Instead, she wanted to pay back Alex for what he had done to her.