Actually, I think it is.
When a man's partner is pregnant, hormonal changes also take place (assuming he wants and expects it). The desire to have sex with other women will often drop. Also, one study found that in the first few months of life, a child looks like his or her father, while another study found that a child looks like a combination of the parents. This seems to be biology's way of telling the father that it's his kid.
So biology intends for monogamous relationships.
Another thing to keep in mind is this: civilizations across the world, divorced from each other until the 1500s, had some form of marriage, which evolved completely separately from each other.