In this instance, I think it's used in parellel with "pivot towards a new passion" to demonstrate an absence of meaning. They both sound nice but don't convey practical information that a person could usefully act on.

More broadly, "time is a flat circle" was popularized in the first series of True Detective, but it originates in Neitzsche's doctrine of eternal recurrence, which was itself influenced by various western and eastern thinkers.

https://plato.stanford.edu/entries/nietzsche/#EterRecuSame