Let us keep the sex part away. Can a man love his wife and his daughter equally? Now if you replace the daughter with another woman, hell breaks loose. I think that a woman will accept her spouse having any relationship with any other woman as long as it doesn't involve sex. Having children exclusively with someone is THE commitment of marriage. The primary purpose of sex IS to have children, not pleasure. Considering that spreading one's DNA is the primary purpose of life, Man will always do it. What about a woman?