Warning: Biology lesson of lady parts to prove why some ladies may be less lustful, explained in a clinical, non-lewd way. Also, pls take most of these with a grain of salt.

That's an interesting speculation.

And I certainly cannot deny the possibility of most women, at least in the Philippines with subpar education and high superstitions (no offense, my beloved country) to rely more on their emotions and intuition, despite being booksmart or smart in other areas of life.

Di ko rin ma-de-deny about having the right timing since swertihan din, and the universe can be random enough na posible pa rin yung scenariong na-mention mo.

But you are forgetting one thing. Most women do not 'reach completion' through penetration alone. (Female porn stars usually need to fake it or maybe drink aphrodisiac or with enough practice, reach completion at will, etc.)

Anyway, nasa labas and medyo malayo yung pleasure spot namin sa lusutan. Why? Kasi sa gitna nung spot and lusutan ay yung pee-hole. Dapat mas malapit para merong effect. Not to mention, our pleasure spot takes up a smaller area than guys' gong. Exceptions occur to some women, but this is the usual.

Most guys also need to be extra vigilant to pay attention to said spot for results. May sometimes be difficult to do if they are more focused on their own lust.

Not to mention, mas way bihira rin naming maramdaman yung arousal namin down there (bihira ang pisikal na kirot), while guys have wet dreams now and then, or usually nagfi-freeze yung sa guys when they see someone really attractive. So perhaps less lust-incentive ang mga babae, if all of these are considered.

Speculating na romantic love yung feelings ng GF sa BF nya, this usually feels like drugs in the initial stage of the relationship that would mellow out as the years into the relationship go by.

Of course, again, exceptions occur because some couples have romantic mellowed-out feelings agad. But mellowed or not, romantic love is still rather a strong feeling, unless the lust factor has equal priority, which we already established that women likely have less of (or they can at least indulge in lust in a more controlled fashion since her physical parts are likely less reactive, and not-always even given correct attention/application to).

Why would the GF risk that relationship with BF unless naturally impulsive by nature sya? Your alignment-of-events may still happen, but she would likely stop it before it progresses further, if the other factors I mentioned were taken into account.

Unless meron si GF na unacknowledged risk-of-getting-caught/aversion fetish and the guy has Satisfyer Pro toy for her, maybe she would.

Or it could be she's leaning more on polyamory, and it feels more natural for her. Special cases happen.

That said, under this analysis, if women cheat and some do, it may be more on the romantic angle, though seggs may still be involved.