I think there is also an amount of self knowledge and character judgment that comes with wanting fidelity. Just wanting to be with a partner who will never cheat on you is not enough. The person who wants that needs to know themselves sufficiently enough to realize what type of people to go for and what type of people to avoid, they should also be good at telling what people are like and will be in the future. There are some people out there who will never cheat because it goes against their principles, moral fiber and their entire nature. There are others who will most likely cheat in the future, but they will work great in partnership with other cheaters, there are some people out there who view cheating or polyamory as normal and the only way to be in a relationship, they couldn't do it any other way. So what shocks some, is a perfectly legitimate way to live for others. The trick is to know yourself sufficiently and realize which people are right for you and which will never work out.
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~