I think I was good that God put it there, they were given the freedom to choose. For example how would I know if my wife truly loves me if I was the only man on earth? Think about it.
That's easy. You'd trust her. Simple as that.
Besides, if she didn't really love you, I think there'd be other signs, such as not really wanting to be with you most of the time, avoiding you, constant arguments, etc.... other men don't even enter into it. I think a relationship with God would be the same way, if one were to compare such a relationship to a romantic relationship.