Like anger which is a divine attribute intended to arouse us to action against injustice, so jealousy is a divine attribute intended to arouse us to actions against infidelity. Just as anger can be abused, so can jealousy -- mainly because in sinful humans, such emotions are not always pure. As anger is the obverse side of God's holiness, so jealousy is the obverse side of God's love. So Paul warns against participation in feasts to demons because it would "arouse the Lord's jealousy" (In 1 Cor 10:22). The more we love, the greater the emotion of jealousy against unfaithfulness and infidelity. It's an emotion given to protect a relationship, not to destroy: it arouses the beloved to action. As much as love is "strong as death", so jealousy is "as enduring as the grave". Even in other love relationships (among friends, parents & children, etc), jealousy can happen when the one who gives love perceives the beloved is giving her/his affection to someone else. As Paul says in 1 Corinthians 13:7, love "always protects."
Marital love calls for faithfulness and fidelity. If we want to enter into such close and intimate relationship, we must be prepared to be faithful "till death do us part." There is no place for half-hearted and conditional commitment. Living together without the public commitment of marriage exposes the relationship to jealousy and hurts. Marriage is a public pledge of commitment and faithfulness and a couple is held accountable to God, to their pastors and the community to remain faithful: "for better for worse, for richer for poorer, in sickness and in health, to love and to cherish, till death us do part, according to God's holy ordinance."
Once married, we are more than just lovers--we become like brother and sister. And such relationship is protective and cannot be broken: "If only you were to me like a brother, who was nursed at my mother's breasts!" (8:1).
Father, help us be faithful to our spouses because we have made a vow before God, pastors and relatives and friends to be faithful unto death. Like brothers and sisters, may our relationship never be broken. Amen.