The premise is suspect.
First, there are lots of (mostly) monogamous animals ('cheating' in monogamous pair bonds gets a fair amount of study).
Second, which gorillas? Are you talking about the ones that form alliances with several males and maintain friendly relationships, groom one another, and fight together against common enemies?
Third, monogamy (even with cheating) seems to have an advantage for species where females forage on their own rather than in groups/herds. There's more to it, though.
This is from a pre-print study, so should be viewed with some suspicion, but it at least describes the current state of investigations:
Since phylogenetic inertia is not a realistic explanation given that four very distantly related lineages are monogamous, the implication is that monogamy has alternative fitness advantages for males. These benefits must also be advantageous for the female, otherwise she would be not willing to tolerate the male’s continued presence – and, perhaps more importantly, would not be willing to undergo the evolution of the expensive cognitive and behavioural traits associated with pairbonding (Dunbar & Shultz 2021).
the fact that primates, in particular, have a long period of offspring dependency suggests that the problem is more likely to be associated with offspring survival.
For human-specific stuff, here's a piece on promiscuity: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3210680/
And one on the ideology of female 'honor' and predictors of who will feel what and how strongly : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10563489/
Look, I don't know if JD Vance had sex with a couch. I don't even know if JD Vance had sex with couch cushions. But yes, I've heard that JD Vance did not WRITE that he had sex with a couch in his book. I don't know if JD Vance wrote he had sex with a couch somewhere else, though.
John Oliver called Vance's staff to ask and they hung up on Oliver, which was reported as 'not a "no"', so I had been thinking, 'ya know? maybe that JD Vance guy really is a couchfucker, who knows?' But here you're saying he's denied it? Or partially denied it? Well I don't know what to think now, but I guess it is safer to presume JD Vance having sex with a couch is probably more legend than fact. Certainly, JD Vance having sex with a couch isn't something you'd want to discuss in polite society or political debate because we've no proof and a possible denial.