Oral sex is documented throughout much of the Roman world. However, it is rarely viewed in a positive light.

Catullus in his Carmen (99:10) refers to the "filthy spit of a filthy prostitute" referring to 'os impurum' or the 'filthy mouth' of those who provide oral sex. It was such a severe insult that Cicero refused to use it on anyone of his own social standing. Martial's 3rd Epigram (3:17) confirms this sentiment. It relays a story of a 'fellator' (one who gives oral sex) breathing on a hot cake to cool it, but his putrid breath turns it into excrement. Martial also jokes (Epigram 7:94) about a man who smells a fine perfume but turns it to 'garum' (a fermented Roman fish sauce) because his mouth was stained from oral sex. Generally, in Roman art, when we find images of oral sex it is reciprocal, as the Romans had a much more dominance focused approach to sex. Cunnilingus was only performed by upstanding men if they simultaneously received fellatio. Otherwise being the giver of oral sex was considered humiliating... Though perhaps this was titillating in it's own right. A wall painting from Pompeii shows a small, furtive man giving oral to a tall, shapely woman. Many of our words for oral sex derive from Latin, such as Fellatio (From Fellō, to suck) and Cunnilingus (from Cunnus, Vulva, + lingō, to lick) and even Irrumātiō meaning literally 'to face-fuck'

Note: Irrumātiō, face-fucking, is considered even more vulgar and humiliating, to the point that Martial (Epigram 2:47) claims that it is what a man should do to a man who sleeps with his wife. Catullus in Carmen 16 even threatens critics of his poems with Irrumātiō, out of anger.

Christianity, with it's criticism of most types of sexuality, really curbed a lot of references to things like oral sex in the medieval period. But I hope that little bit on the Romans helped!