prostitution exposure is a speculation inspired by the timeframe and lifestyle.

impotency:

from the wiki: "due to his impotency he would frequently murder his sexual partners for psychosexual reasons."

from his dialogue: "succulent little whores. i'll show you flaccid."

from his dialogue: "bambino. The indignity of it. how's a man supposed to... perform."

from his dialogue: "call me impotent? call me little?"

from his dialogue: "what, you think i can't get it up? come out, i'll show you."

parental abuse:

from the wiki: "the deformations of his skull and face are the result of both a birth defect, and frequent physical abuse from his father."

from the wiki: "his aggressive and explosive nature reflect a deep-seated insecurity, stemming from his abusive childhood and his feelings of sexual inadequacy."

from his dialogue: "who is that? my dad send you? think I'm fucking scared of you?" implies fear of his father due to the abuse/near-death experience.

from the document, "Age Twelve":

from the Murkoff Chronicles, Issue 3: in response to the previously mentioned murder.

from the Murkoff Chronicles, Issue 3: in response to the affair.

franco's age vs angelina's age:

from the wiki: "he (salvatore) married angelina - a woman much closer in age to his son..."

from the document, "AKA Il Bambino":

from the document, "Age Twelve": also significant here.

from the document, "Get Barbi": year of collection will help with calculations.

from the Murkoff Chronicles, Issue 3: the photo depicts a ten year-old franco. the photo was taken fifteen years ago. by previous accounts, that makes him 25-27 years old in 1959. depending on which you go with, he turned 18 in 1950/52 and 21 in 1953/55.

from the Murkoff Chronicles, Issue 3: this "cuban situation" (presumably when fidel castro came into power) began in january, 1959. angela was "only a couple years older than franco" at the time of their affair.

from the document, "Counter Revolutionary": confirming franco's involvement in the cuban community/helping "mutual friends" suggests his exile occurred sometime during 1959 (the CIA wasn't involved with cuban affairs during the 1953 revolution, but was when fidel castro assumed control). as there is no reason to assume the affair was kept secret for years (and it's highly unlikely it would have remained secret all those years, anyway), i estimate it occurring in 1957 at the earliest. this would make franco 23-25 years old when he slept with angelina.

franco's relationship with women:

from the wiki: "franco engaged in a sexual relationship with his stepmother angelina barbi, as her degradation brought him sexual pleasure."

from the wiki: "franco is also extremely sexually depraved in nature and takes pleasure in murdering out of arousal, killing one of the female Giants and engaging in necrophilia with her corpse."

from the wiki: "his aggressive and explosive nature reflect a deep-seated insecurity, stemming from his abusive childhood and his feelings of sexual inadequacy."

from the wiki: "barbi collects nipples".

from his dialogue: "she didn't have to laugh at me. she didn't have to do that." unclear who "she" is.

from the document, "AKA Il Bambino": also significant here.

from the document, "Age Twelve": also significant here.

from the document, "The Gator Hook":

from the document, "Honey Island":

from the document, "Angelina":

from the Murkoff Chronicles, Issue 3:

from the Murkoff Chronicles, Issue 3:

from the Murkoff Chronicles, Issue 3:

the events following the affair:

from the wiki: "franco's father found out about the affair and severely beat him before exiling him, his life spared due to their blood relation."

salvatore and killing his wives:

from his dialogue: "i never knew my real mother."

from his dialogue: "my father killed my mother, you know that? doctors? you listening? i had a new mom every year..." hyperbole, but still significant.

why i believe he could consent/pursue angelina:

from the wiki: "despite his disability and sustaining injuries through both his field of work and domestic abuse, he remains in otherwise excellent health and physical condition."

from the wiki: "barbi's midface hypoplasia, enlarged cranium, and laboured breathing are features reminiscent of those seen in people born with pfeiffer syndrome type I."

from the cleveland clinic: "children diagnosed with classic pfeiffer syndrome usually have an average life expectancy and typical intelligence with treatment." from the boston children's hospital: "most of these children have normal intelligence and a normal life span." my point in sharing this is that pfeiffer syndrome type I, which franco is most likely to have, is not an intellectual disability.