While her husband was away on military campaigns, she fell in love with Curzon Dax and they had an affair. Curzon had promised Enina that he would keep a vow of silence about their relationship, and this carried over to the next host, Jadzia.
The secret was only revealed when Ilon Tandro visited Deep Space 9 space station in 2369, believing that Curzon was the one who betrayed his father to the rebels as he had been the only person with the necessary knowledge and no clear alibi, and wanting to accuse Jadzia of Ardelon's murder (In reality, Ardelon had been intending to betray his own forces to the rebels and been killed). Enina, after being persuaded by Odo, went to the station to Jadzia's extradition hearing to reveal the truth about her affair with Curzon, confirming that Curzon couldn't have killed Ardelon as he was in bed with her at the time her husband was murdered. (DS9: "Dax")