No, it's not. It's never certain. I can say in all honesty that I've never cheaten on my wife since we're together.
I do speak for myself now though, I know there are men who cheat, but there are also a lot of men like me, who don't.
But, if you live in your relationship with the idea that he will cheat you anyway, and that you'd better deal with it, it will show in your relationship. You will never be fully 'into' it, because you are afraid to get hurt. And if he feels that you are not really into the relationship, he might go looking for that elsewhere.
That's what is called a self-fulfilling prophecy, or manifestation. It happens because you think it will.
But be careful, this does NOT mean that if your husband cheats on you, that it is by definition your fault! Nor is this an excuse for men to cheat! What I mean to say is that if you want a loving and healthy relationship, you both need to be in it whole heartedly.