ON THE PASTORAL CARE OF HOMOSEXUAL PERSONS 1986
The Church, obedient to the Lord who founded her and gave to her the sacramental life, celebrates the divine plan of the loving and live-giving union of men and women in the sacrament of marriage. It is only in the marital relationship that the use of the sexual faculty can be morally good. A person engaging in homosexual behaviour therefore acts immorally.
To chose someone of the same sex for one's sexual activity is to annul the rich symbolism and meaning, not to mention the goals, of the Creator's sexual design. Homosexual activity is not a complementary union, able to transmit life; and so it thwarts the call to a life of that form of self-giving which the Gospel says is the essence of Christian living. This does not mean that homosexual persons are not often generous and giving of themselves; but when they engage in homosexual activity they confirm within themselves a disordered sexual inclination which is essentially self-indulgent.
As in every moral disorder, homosexual activity prevents one's own fulfillment and happiness by acting contrary to the creative wisdom of God.