Women choose men based on their suitability to raise children. As many have said, the goal of sexual promiscuity is hypergamy, sex is never the goal for women. Love is a bias that will exaggerate your better points, and it certainly helps, but it doesn't last.

Cheap, effective contraception has reduced the risk of promiscuity from prenancy to just STIs. This enables a woman to cheat. (Contraception is no guarantee however, so for the man, there is always a risk of being cuckolded.)

So, take the fact that children are the goal for women. When a woman is pregnant, she can be assured that the child is hers. Women don't worry about paternity, instead, they worry about keeping the man loyal so that he can fulfill the traditional roles of provider and protector. If she manages to be successful in this, then everything else is fair game, including other men. The sexual promiscuity of other women however works against her own interests, as she is now under a bit more pressure keep the man loyal. Personally, I find the fact that women's liberation has turned women into their own biggest threat hilarious.

For the man, the return on the investment of monogamy is the assurance that any child is his. It's a high cost and historically there's been no guarantee. Nowadays of course, you can get a paternity test. Make no mistake, if you end up raising someone elses child, you've lost both genetically and socially.

Woman are looking for someone to help raise children, even if they don't know it. So it's a fair assumption that women want a man who can provide and protect. Assuming that women are now paid the same amount for the same work, "provider" now means having a higher paying job. It's a bit obtuse to show a girl your paycheck, so hold obvious signs of wealth (i.e. the latest phone, car and house keys). Also, never move into the girl's place, as it reduces your role as provider and thus SMV. Letting your girlfriend move in with you might make it more difficult for her to cheat on you, but it also puts a financial cost on breaking up. If you're not happy with the risk, don't let her move in.

I'd say the role of protector nowadays has equal or greater importance, so hit the gym and show it off.

Maybe this is aloo controversial, maybe it's obvious, I can't tell anymore. Comments/corrections welcome.

TL;DR: women choose men based on their suitability to raise children, even if they're not interested in children.