-Romans 3:23, KJV
While every human being is a sinner, that does not mean every human being has committed the same sins.
Capable does not mean actual.
The divorce fear-mongers tell faithful spouses essentially not to hope for a future partner who treats them better than their current adulterous spouse. They suggest it gets no better. It is just different.
I can attest from personal experience that this is false. It does get better. And yes, you can find a partner–in time–who will not lie, cheat, gas-light, and otherwise abuse you.
Divorce is not the end of all hope for a healthy future marriage, in other words.
We are all capable of cheating upon our spouses–assuming we are married–but that does not mean we all will do so. Plenty of humans have gone their whole lives in monogamous relationships without a single incident of abusive infidelity.
Such people do exist.
Some people actually take their marriage vows seriously–especially, that forsaking all others for a lifetime part.
And others do not–i.e. our cheaters.
Not everyone is a cheater even if everyone–who is in a relationship–has the power to be so. If we didn’t have that power, then it would be pointless to make such a vow of lifelong fidelity at the wedding altar.
The difference is character. Some people have it, and others–i.e. our cheaters–do not. And yes, single people with character exist even if our current or past partner did not have it.