Jealousy is an enduring topic of interest for psychologists and theologians since ages.
Jealousy is a reaction to a perceived threat--real or imagined--to a valued relationship or to its quality.
Unlike envy, feelings of jealousy always appear to stem from one's sense that something about their life is not secure, e.g., is uncertain or in danger.
In some cases, the insecurity is not founded on realistic dangers to the relationship.
When a person is jealous, the lines of communication gets murky and problems begin to stem from the lack of appropriate communication.
The best way to overcome jealousy is to face your feelings and openly talk about it with the intention to bring about a positive outcome.
According to this Discovery article, human jealousy has roots in our reproductive past and has probably endured because it serves its ultimate purpose, to help ward off potential rivals.
Jealousy produces tremendous pain and distress for people and it is important to quickly turn to positive communication in order to avoid lasting damage to relationships.