I see jealousy as a painful but valuable form of perception. It is the detection of estrangement, real or possible, and the disruption it inflicts on the self.
There are at least three ways to avoid feeling jealousy, each a strategy against estranging disruption.
The first, most obvious one is that your relationships are on solid ground and are not currently at risk of estrangement.
A less obvious one is that your relationships are so impersonal that estrangement is the norm, and therefore not a threat. Incurable loneliness, emptiness, depression and irritability is the consequence. But these consequences of impersonality can become normal, too, and produces a worldview that experiences life itself as essentially impersonal and meaningless, just a play of social forces creating and animating social agents, who strive for power and mistake superstructural mental artifacts for souls.
The last one is that you and those with whom you relate are integrated within a social structure that keeps everyone in stable, fixed and familiar relationships with one another. Held in place and in shape within a complex network of interpersonal bonds and social associations, nobody is in danger of total estrangement. This stability, however, comes at the cost of personal freedom.
To encapsulate each cause in a word, defense against jealousy can come from intimacy, politics or culture.