I think, and the Church has traditionally taught, that the “sin” isn’t being homosexual, it is engaging in homosexual acts.
The inherent orientation, strictly in itself, is not sinful if the individual had no part in its creation. Any conative thought processes, however, including fantasies that are under the individual's control, may be sinful. The thoughts need not be acted upon. This goes for heterosexuals and adulterous fantasies, etc., as well.
We do teach that, but it has been decided that homosexuality is a disordered condition, and is not what is needed in the priesthood. Remember, part of the mission of the priest is to form and shape his congregation, and we don’t need homos shaping the CYO.
Real simple, Cammie.
Homosexual act= sinful
Homosexual orientation = not sinful but intrinsically disordered.