The Catholic Church teaches that contraceptive sex within marriage or sex outside of marriage is not an act of love. Homosexual sex, a form of mutual masturbation, is closed to both life and the permanence of marriage. Immoral sex is a mortal sin that stops the infusion of divine charity.
In his 1968 encyclical Humanae Vitae (HV), Bl. Pope Paul VI taught that contraception within marriage separates the procreative aspect of life and the unitive aspect of love. Many Catholics misunderstood Paul VI to mean the unitive aspect of sex (love) remains even when procreation (life) is blocked. The Church teaches, however, that destroying one destroys the other.
In paragraph 12 of HV, Paul VI re-presented previous magisterial teaching by reaffirming the "inseparable connection ... between the unitive significance and the procreative significance which are both inherent to the marriage act." He further taught, "[If] each of these essential qualities, the unitive and the procreative, is preserved, the use of marriage fully retains its sense of true mutual love." The reverse is also true; if the essential quality of procreation isn't preserved, then the use of marriage doesn't retain its sense of true mutual love.
Pope St. John Paul II made this point in his 1984 reflection on paragraph 12 of HV:
[The] conjugal act signifies not only love, but also potential fecundity. ... [It] is not licit to separate the unitive aspect from the procreative aspect, because both the one and the other pertain to the intimate truth of the conjugal act.. ... Therefore, in such a case the conjugal act, deprived of its interior truth because it is artificially deprived of its procreative capacity, ceases also to be an act of love.
Sex devoid of permanence is likewise devoid of its unitive or love-giving aspect. Fornication, adultery and homosexuality are, therefore, absent true charity and make each person an object of use rather than a subject of sacrificial love.
Explore the impact sex has on society in season one of Church Militant's premium show Right Reason—Sex and Civilization.