Fidelity and idolatry

In the first reading today. St. Paul equates fornication and promiscuity with worshipping a false god in Eph 4:32-5:8. I think it has to do with fidelity or faithfulness. We know of God declaring himself to Moses as a jealous god, and jealousy comes up in exclusive relationships. What else is as naturally and normatively exclusive as marriage, even without considering religious norms? Moses allowed for divorce, but Jesus made a point to reverse that. Why? St. Paul identifies marriage with the relationship between Christ and his Church as a sacred covenant of love. It is a self-donating relationship which makes the two united as one. Since marriage is an image of this sanctified unity -- more than a mere image, but a reality -- then fornication, which is opposed to this exclusive, sacred bond, is a betrayal of the true worship, substantial relationship, of/with the God-man, Jesus Christ. It defies the ideals of commitment, consecration (setting apart) or holiness, and, of course, fidelity. A lifestyle of fornication cannot allow for commitment to a faithful union with a one and only, and a secret life of promiscuity will simply destroy any standing vows of commitment as well as the heart of the one vows were made with.