You are correct. The Roman Catholic Church condemns the sin of engaging in homosexual behavior and calls on homosexuals to be celibate. Aside from the homosexual act being sinful, it is also adultery, because adultery is having sex with any person out of wedlock.
Main Entry: adul·tery
Pronunciation: &-'d&l-t(&-)rE
Function: noun
Inflected Form(s): plural -ter·ies
Etymology: Middle English, alteration of avoutrie, from Middle French, from Latin adulterium, from adulter adulterer, back-formation from adulterare
: voluntary sexual intercourse between a married man and someone other than his wife or between a married woman and someone other than her husband; also : an act of adultery