Lifetime monogamy is not natural. However, if you marry with this fundamental understood as a requirement, stay the course and don't cheat.
Me, I'd strongly suggest a majority of men DO NOT marry.
The pain and frustration you experience when you've grown beyond tired of fucking that same old pussy, decade after decade, is extreme. It will make you angry and bitter. Your relationship will erode. It's inevitable.
If you come to love a woman and desire her romantically, ride that wave for as long as it lasts. But do not marry her. If she becomes the woman with whom you choose to have your children, do marry her, but know your sex life will deteriorate gradually until, sooner or later, it will no longer exist. Wanking will be your only saving grace.
But your children don't deserve a sneaking, lying father.
Life is cruel. It is hell.
Best to stay single, engage in an honest sexual experience where available, allow maturity to inform you of your honest appraisal of fatherhood, avoid drugs and booze, and keep a majority at arms' length. Humans are dangerous. Extremely dangerous.
Our sex drives are a curse. Know this.