There is a very common view among the fair sex that sex is validated by romance. In other words, if a woman is in love with a man, then sex with that man is justified. Commitment is desired by women, but it is not required for sex. Neither is marriage required by many women. For many of the distaff sex, romantic feelings are sufficient reason for a poke with an amorous phallus. Of course, marriage vows used to be the requirement for sex under the Patriarchy, back when the legal system would have enforced those vows. However, the legal system will now only enforce a redistribution of assets when a divorce occurs. It’s very handy for women to be able to divorce their sexual ethics from the onerous burden of a patriarchal legal system.
NB: A pickup artist would view this ethic as “Tingles validates sex for a woman.” He would see the woman’s love feelings as tingles (sexual/romantic attraction).