While trying to understand the root of my own personal feelings of romantic jealousy, I came across a video called "Primal Instincts: Male Scarcity Mentality and Mate Guarding"
In this video, the youtuber HappyHumbleHermit explains that, to understand jealousy and stingyness in men, it is useful to observe nature. In most species, the female gives sexual access to the male. Family size and sexual access are both regulated by the female of the species.
While the female decides who to give sexual access to, the male builds up testosterone, which is one hell of a hormone. High levels of testosterone allow males to pursue the female to extents that may even harm the male. Female mantis and black widows are infamous for cannibalizing on their male partners.
In the above video, female polar bears will mate with a partner for as long as he can sustain fighting off other suitors. By guarding his female, the male polar bear is ensuring that the conceived cubs are of his genetic line. When the male no longer can keep up with competitor pursuers, the couple part their ways.
In humans, these male instincts may have become domesticated, but not eliminated. Chivalry, for example, is putting the female partner before oneself. Opening a door for a girlfriend may not be as sacrificed as allowing your mantis partner to behead you, but it may well be a sublimation of those mate protection instincts that males have evolved, as a result of the economics of reproduction:
While men produce millions of daily spermatozoa, women produce only one ovum per month. Women must consider carefully whom to give sexual access to, and in some cases, this may transform into a dual mating strategy, where one man is taking care of kids he doesn't know are not his own.
In the current year of third wave feminism, women have been sexually liberated from the economics of reproduction. Via contraceptive pills, women are allowed to regulate their reproduction, meaning they no longer need to hold for Mr. Right to put out. Women are becoming more adventurous and risk takers in the realm of reproduction.
The problem is that there is still no pill to liberate men from their mate protection instincts, which makes for much frustration and failure in current year's couples. Specially in younger males, you may find various coping mechanisms to deal with these male instincts. From roleplaying Mario rescuing Princess Peaches, to numbing with drugs and alcohol, to going MGTOW, men seem to be in a mission to avoid the stressful tension of current year's romantic jealousy.
