Randyman is right. I would go further and say that authentic jealousy is, unlike envy, a relatively rare and complex emotion that stems from our insecurity about how much the people whom we cherish reciprocate our regard. It usually involves a lover, but I sometimes feel it around any kind of superiors: if they express high esteem for us, we don't want them turning around and expressing exactly the same esteem for just anyone else. Once they have returned some of our affection, we want to be the exclusive apple of their eye. Such possessiveness can be dangerous, but it seems to accompany most feelings of love -- any love, that is, other than the extremes of complete security or complete abjection.