Actually, Jude refers to angels fornicating.
"6 And angels who had not kept their own original state, but had abandoned their own dwelling, he keeps in eternal chains under gloomy darkness, to [the] judgment of [the] great day;
7 as Sodom and Gomorrha, and the cities around them, committing greedily fornication, in a like manner with them, and going after other flesh, lie there as an example, undergoing the judgment of eternal fire."
In the Greek, "with them" is masculine, so "with them" can't be referring to the cities, which are feminine, but rather "angels", which are masculine.
http://www.scripture4all.org/OnlineInterlinear/NTpdf/jud1.pdf
It could just be a reference to the story and not a complete endorsement of the story?