In the series Mindhunter, there is a story arc in which Debbie is caught (emotionally) cheating on Holden. See this answer for a good summary.
This story arc starts and develops over a single episode, culminating in
the relationship breaking apart, with Debbie chasing Holden as he leaves the building.
At the very start of the next episode, the story arc is wordlessly closed off, seemingly with no effect on the rest of the series. It is never mentioned again, and the state of the series is returned to how it was before the story arc began. The viewer is never given a resolution to the issue, leaving it as a loose thread.
What is the purpose of including this story arc in the series?