Jealousy: noun - overwhelming fear, suspicion, or belief one is, or might be, displaced in someone's affections; distrust of the faithfulness of a spouse or lover; of God - His intolerance of the worship of other gods (which has always struck me as an odd quality in a being supposed to be omniscient and almighty); resentment or envy of another person or his or her possible or actual success, advantage, or superiority; rivalry; concern or anxiety for the preservation or well-being of something or someone; vigilance or care in guarding something or someone.
Envy: noun - feeling of resentful or discontented longing aroused by another person's better fortune, situation.
As is so often the case with alternatives in English, its vocabulary culled from so many different languages, there is some overlap in the meanings of these two words. However, jealousy is generally used to convey the emotions felt in areas of possession and protection, and envy generally expresses a desire to actually have what the other person has (instead of them, rather than as well as).
‘One day, your insane and unfounded jealousy will drive a wedge between us, destroy all the love I feel for you, and send me out of your life for good.’
‘Mary guarded her new baby with that jealousy only the new mother knows.’
‘Derek was consumed by envy of his neighbour to the extent he plotted murder so that he might take all those things he thought the man had but didn’t deserve.’