As Barmaid says, jealousy and envy are two very different things.
For example, if I see a report that someone has won a massive amount on the National Lottery, I might well envy that person but I'll not have any negative feelings towards them.
On the other hand if someone stole my girlfriend away from me, while I might envy him for having her, it's likely that I'd also feel strong negative feelings towards him. It in situations like that, when envy is overlaid with negativity, that it then becomes jealousy.
Actually though, while I may have envied many people in my life, I don't think that I've ever really felt true jealousy towards anyone. I'm the sort of person who can simply shrug their shoulders, taking whatever life throws at me and simply saying "C'est la vie!".
So I'm possibly not the best person to be answering your question,Jennyjoan!