In order to keep the affair private, Thena kidnapped (!) an infertile woman and placed the babies inside her womb (!!) in order for the babies to be born as humans.
However, there was a point when things ended badly, and Thena thought her relationship with Kro was truly finished.
Eventually, Thena and Kro made love, and Thena was pregnant with their two children.
But sure enough, Kro proved to be surprising long lived, certainly for a Deviant, and there was a reconnection between them around World War II.