Right, research and common sense and basic human experience backs this up.
Cheating takes the sort of person who is quite willing and able to lie persistently and repeatedly to a person who loves and trusts them as well as being willing to put their sexual health at risk.
It shows a deeply unethical character and low morals. It shows a true contempt for the person who loves and trust's them basic rights.
This is not a case of a kid swiping a chocolate bar in the supermarket and it's not a "mistake". It actually takes a certain lack of empathy, kindness, consideration, normal human feeling, it takes a cold hearted, unkind, entitled and unethical person to cheat.
And it's not normal. 4o out of 5 men do NOT cheat, and women cheat even less. Something like 20 percent of men do cheat and 13 percent of women. NOT the majority, and not actually normal.
That tallies with what we know about people. If we lived in a society of lying, abusing cheaters where treachery was normal we would be well and truly fucked.
Cheaters have done a great job of making everyone think betraying your partner is normal and try very hard indeed to minimise how loathesome cheating is.
But they are very much in the minority, it's not normal to treat someone like they just do not matter and have no rights and as such because it is an abnormal trait, it goes deeply to character. It's not naughty or even bad behaviour - it is a character trait. The people who cheat are untrustworthy in their very core.
And we all being sly, unethical, unkind, low empathy and entitled doesn't suddenly shift because you get older. You don't meet someone who is lacking in compassion and ethics at age 25 who suddenly becomes empathetic and ethical aged 50 - that would be vanishingly rare.
So yep, cheaters are stable in their low morals and ethics, and it would be dangerous to stake your happiness on them being the rare one that breaks the mould.