Hmmm, let's see. Eos is jealous of Cephalus's wife, Procris, whom he truly loves. Procris is jealous of Eos, who whisked her husband away and in some versions of the story succeeded in seducing him. Cephalus is jealous of... well, himself really, since he manages to kind of seduce his wife while disguised as another man. The easier question would be who isn't jealous in this myth?
In the end, jealousy leads to tragedy when Cephalus accidentally kills his wife while she's spying on him. If you're going to try to pull a moral out of this one, it might be that jealousy—in any shape or form—is massively destructive.
Questions About Jealousy
Why is Eos jealous of Procris? Can't she have any man she wants?
In what ways does misinformation fan the flames of jealousy in this story?
Does Cephalus have a right to suspect his wife? Why or why not?
Does Procris have a right to suspect her husband? Why or why not?