I'd disagree with that definition. Envy is about jealousy; desiring another's good fortune for yourself. "Envy denotes a longing to possess something awarded to or achieved by another".
What you're describing, unhappiness about another's good fortune, is simlpy malice. One simply doesn't want another to have good fortune.
In the case of envy, you don't instrinsically mind that another has good fortune; the point is that you want it, too.
With that in mind, I'd suggest the opposite of envy to be generosity. Instead of wanting what others have, you're happy to give away what you have.
Seconded! You hit the nail straight on its head imo, Morrus.
