Zero Two loved Hiro before she realized he was truly her darling(Splr)
In Episode 6 "Darling in the Franxx" Hiro was anticipated to die. He did for a moment, but long story short he did come back to save Zero Two.
Offtrack for a moment: It seems as if she didn't really care about Hiro, in a comment made in the previous episode when she was talking with Ichigo saying that if he died "he wouldn't have amounted to much" then later she would call him fotter, which is a term to describe someone being used. Even though she was affectionate and playful with him before, she didn't seem to truly love him until the memories of their past came back to them, more than less to Hiro.
This sort of bothered me, that she was treating him like another Stamen to be consumed. But then I realized, in episode 6, first of all that when Hiro was passing on that when he saw Zero Two she looked "so sad." Then after Hiro supposedly died and she began to stampede. She was screaming that "you are nothing but a monster!" It can be interpreted that she was screaming at the massive beast smashing her and the stampeding Strelitzia, but I think she was tormenting herself when she thought she killed Hiro, even before she knew he was her true darling.