Official Catholic teaching requires that homosexual people abstain from sex. But the Catholic Church also teaches solemnly that people are obliged to form their conscience carefully and responsibly and to follow it as the bottom line in every moral decision.
Neither Scripture nor Tradition nor natural law theory nor human science nor personal experience convincingly supports official Catholic teaching about the immorality of homogenital acts. Accordingly, and after much soul-searching, many gay and lesbian Catholics have formed consciences that differ from official Church teaching and have entered into homosexual relationships. In this respect they are exactly like heterosexual married Catholic couples who cannot accept Vatican teaching on contraception.