Economic principles can be applied outside of economics, viewing it as Praxeology instead of Economics. This is true even in the case of intimate relationships, where economics can be used to analyze certain aspects. This does not mean, as critics of libertarians often wrongly say, that libertarians put a price tag on everything, but only that the principles can be used to gain greater insight.
One part of analyzing intimate relationships is to help solve the riddle of the old complaint that men who sleep around are not condemned the way women who sleep around do. It is an old complaint about a double standard. There is, however, such a thing as a male slut.
Reducing intimate relationships to their simplest form, men trade love for sex and women trade sex for love. This model borders on over-simplified, but not quite. It does ignore as irrelevant all the various characteristics any individual might seek in a partner. It also leaves out the relevant aspect that women also seek sex and men also seek love, but it leaves it out for the sake of creating a simpler model.
Viewed as a transaction, men giving love to gain sex and women giving sex to gain love, one can see where the criticism of the slut comes from. Any person who gives a valuable commodity away without charging for that commodity is looked down upon, and receiving it from that person is not considered as valuable as if it had been traded for.
Also given that perspective, one can immediately see what it would take for a man to be seen as undercharging. Such a man is known as “the nice guy.” Youtube commentator GirlWritesWhat has a video about how women, especially feminists, look down upon nice guys, because what they are doing is giving away all the emotional support that normally would cost a woman a relationship with the man.
Just as men seldom seek actual long term relationships with woman who are physically intimate too early in a relationship, women seldom seek actual long term relationships with men who are emotionally intimate too early in a relationship. The reason people don't get a quick answer to the question "where are the male sluts?" is because the term needs to be defined, and economics helps with that.