In case you skip it...

This episode establishes that in Trill culture, it’s taboo for a joined Trill to resume a romantic relationship with someone that the same symbiont romanced while joined with a different host. Doing so is called “reassociation” and it results in exile from the Trill homeworld, which means that the symbiont will never be transferred to a new host and will die with their current one. This comes up through Dax running into someone she’d been married to in a previous life, being tempted to rekindle their love, and ultimately not getting to do so.

Like most new things we learn about Dax and the Trill, this comes out of nowhere, appears to conflict with earlier information, and is poorly explained. Trill should be a lot more interesting than they are, but their worldbuilding is so slapdash that after all this time we have barely any idea what their culture is actually like.

In case you were wondering why I keep suggesting to skip the Trill episodes.