It's no fun to feel envy or jealousy because both make you feel inadequate. Envy is when you want what someone else has, but jealousy is when you're worried someone's trying to take what you have. If you want your neighbor's new convertible, you feel envy. If she takes your husband for a ride, you feel jealousy.
Envy requires two parties, like you and that neighbor, when you want her new car and you wish you were the one riding around with the top down. You feel envy when you want something someone else has:
Tall and lean, he is wearing blue jeans, tennis shoes, a dark blazer and red tie with hair every sports anchor would envy. (Chicago Tribune)
"There be many, Judith," said he, "who might envy you your health and good spirits." (William Black)
Jealousy requires three parties, like you, your neighbor, and your husband, when not only do you wish you had that cool car, but you're worried your husband is going to ride off into the sunset in it without you. Jealousy is exciting because it shows up in lovers' triangles and Shakespeare's plays:
In Shakespeare, Othello is doomed by jealousy, Lear by pride. (Slate)
The peasant, mad with jealousy, ended by driving an awl into his chest. (Fyodor Dostoyevsky)
Professional jealousy, tortured artist blues, Spinal Tap-ish excess and other clichés abound, but nobody seems to notice. (The Guardian)
You can feel envy about something you don't have but want, but you feel jealousy over something you already have but are afraid of losing, like that husband who's always hanging out next door.