Ezri Dax (Nicole de Boer) didn't have much of an opportunity to develop as a character during the final season of Star Trek: Deep Space Nine. She'd gained Jadzia Dax's symbiont along with all her memories. Though that brought her and Worf (Michael Dorn) together briefly, ultimately, she and Dr. Julian Bashir (Alexander Siddig) fell in love. But there was no indication what happened to their relationship or either of them at the end of the series.
Lead story developer, Ira Steven Behr, answered that question unofficially in What We Left Behind: Looking Back At Star Trek: Deep Space Nine. [via Gamerant] Both Ezri and Dr. Bashir remained at Deep Space Nine for several years after the conclusion of the Dominion War. Presumably, Ezri was being promoted regularly as she would later become the captain of her own starship. And Dr. Bashir would become the Chief Medical Officer aboard that ship. Apparently, the rules about fraternization only existed in Star Trek: The Original Series as each series after that had no problem letting crew members become involved.
Behr went on to say that the couple stayed together for the remainder of their lives, but Ezri's memories would remain intact in the symbiont long after both she and Dr. Bashir pass away. It's a sweet ending, especially for Dr. Bashir as he hadn't had any luck with love at Deep Space Nine. Originally, he'd been attracted to Jadzia Dax, so it seems fitting that he spends his life with the symbiont that carried her memories.