It is de rigeur - a given, part of Mafia culture - for a Mob guy to have or more gumars.(mistress). But, neither Vito nor Michael seemed to have had one, or even been unfaithful to their wives. The novel says Vito was "notoriously straightlaced in matters of sex," and disapproved of Fredo carrying on with cocktail waitresses. In GF, Fredo arranges for several showgirls to entertain Michael when he arrives at Moe Greene's hotel. Michael's hostile: "Who are the girls, Fredo?" and tells him to get rid of them,

Why do you think that was?

I reckon they didn't consider themselves as Mafia
Vito was the Justice league saving Italian Americans and Michael the legitimate businessman

My take, Vito and Michael would have considered having gumars or cavorting with showgirls as a weakness – we all know what happened to Tattaglia, Carlo and Geary.....

Sonny's “sexual excess” made Sonny rash that Sonny still took the risk visiting his gumar Lucy during the gangland warfare, parking his car outside Lucy's apartment block even with buttonmen on guard duty

“Fredo's sexual excess” banging cocktail waitresses two at a time got Fredo slapped around in public by Greene

Could be. After Sonny shot his mouth off at the Solozzo meeting, Vito said, "I think that comedy you play out with that young girl is making your brain soft."

I think that some men are just born different. Vito didn't grow up around the mafia and it's not like he was Henry Hill with the: "As far back as I can remember, I always wanted to be a gangster." For him it was more of a necessity of getting involved in crime, so he had a different mindset than other people.

When it comes to Sonny and Fredo, they had some qualities of Vito, but not the one that Michael picked up (being an "honorable, respectable" man to his family). We can see that with Sonny screaming at the dinner table and discussing business ("Papa never talked about business at table...") etc.

The same way with civilians. Some men cheat, some men don't. I think Vito and Michael were one of those that didn't.

Much like Bobby Bacala & Johnny Sac in Sopranos.

My two cents at least.

I guess you could argue Apollonia because Mike was still technically with Kay when he fled. Yes I know he married Appolonia in Italy but that’s the closest thing I could think of.

Good assessment of it.

I think Lana and CleanBandit nailed it!

some do some don't too simplistic

I reckon Some men cheat, some men don't because some men are just born different is no excuse
It is oversimplifying and justifying infidelity

The women too for whatever reason whether money, being gangster moll, they become gumars for gangsters or civilians knowing the men are married

Vito the "honorable, respectable" man to his family but still turned a blind eye to his son, cheating on his wife and only mentioned his gumar only when Sonny shot his mouth off at the Solozzo meeting I reckon nothing "honorable, or respectable about that

only mentioned when affected business