When people have sex, the woman is in a much more dangerous place than a man.
Having a baby for a woman is very costly. She needs someone to protect her while it happens and to help raise the child.
The cost for a man is very low. He only needs a couple minutes to do his part in making a baby, then he can leave at any time.
So with that in mind, lets say the scenario is like this:
If a man impregnates a woman and he stays, the chance the baby survives to reproduction is 90%.
If a man impregnates a woman and he leaves, the chance the baby survives to reproduction is 10%.
So with those statistics, the man is actually in a very advantageous position.
As long as he impregnates 10 or more women in his lifetime, he is ahead than if he had stayed with the same woman for all his life.
Of course, the more healthy the woman, the more likely the baby is to survive even if he leaves. Beauty = healthy in evolutionary terms. If the woman is pretty, maybe she can even get another guy to raise his kids for him! So men seek beauty primarily.
So for a man it is genetically superior to impregnate multiple women (which generally means not staying too close to any of them).
A female on the other hand, can only have children a few times in her life. And she only gets a few shots at it.
If the man leaves, her shot is very likely to end up in failure.
So the woman needs to be very picky about who she has children with. She needs to judge his character, to see if he will stay with her and raise the child. And defend her, fight off aggression, etc..
So to a woman, character is more important than beauty, because that's what determines if her genes survive or not.
Erotic fiction is a billion dollar industry and the vast majority of buyers are women. Manly man stories = porn for women.