Robert Briffault was a surgeon originally from either France or London (his true nationality remains unknown) who later became interested in biology and anthropology. He became a social anthropologist and was known as an accomplished novelist as well.
He published his most well known work called The Mothers: A Study of the Origins of Sentiments and Institutions.
More than a study on matriarchy, it is an essay on the history of family and gender relations. The most relevant aspect of this book is the huge amount of ethnographic information (about customs and beliefs) that it presents.
This book contains family history, gender relations and marriage, matriarchy (matrifocal or matrilineal societies), sociology, ethnology, anthropology, maternity, matrilocal marriages, matrimonial customs, traditions of numerous human groups, etc; but it also engendered what we know today as Briffault's Law which reads as following:
“the female, not the male, determines all the conditions of the animal family. Where the female can derive no benefit from association with the male, no such association takes place.”
The reason I'm sharing this is because I've read many questions on gag that could easily be answered with Briffault's Law in terms of relationships and male / female behavior.
We shouldn't forget that even though we reason very unlike the rest of the animals we are still animals placed in a taxonomic group, and in many contexts, specially when it comes to reproduction those animalistic traits come afloat.
Lets look at the three corollaries of Briffault's Law:
1. Even though a woman has accrued past benefits from her relationship with a man, this is no guarantee of her continuing the relationship with him.
Women hold the power in the mating game and they always will since, as well all know, it is women who give the green light or red light to any advance or propositions from the males. But going a bit further, women also expect for the male to comply to her and provide. If no benefit is gained from an association with a male she may abandon the relationship or simply move forward, and look for someone else.
Kinda like this penguin did...
2. If a woman promises a man to continue her relationship with him in the future in exchange for a benefit received from him today, her promise becomes null and void as soon as the benefit is rendered.
Women DO NOT establish a relationships with men if they see no benefits from establishing the relationship. It is important to note that we aren't talking about money here, not exclusively at least, but women usually go for the highest bidder available for her to establish a relationship and follow her directionality. She could be interested in status, physical appearance of a man (good set of genes and traits), emotional fulfillment, security, etc.
3. A man’s promise of a future benefit has limited ability to secure a continuing relationship with a woman, and his promise carries weight with her only to the extent that the woman’s wait for the benefit is short and to the extent that she trusts him to keep his promise.
According to Briffault, you aren't in safe territory when establishing a relationship with a woman. This is probably the reason why women prefer commitment / marriage over more casual interactions like friends with benefits. This doesn't mean women will not engage in casual sex or having fuck buddies, but this is either temporal or the least when they aren't looking to establish and pursue their biological imperatives.
All in all for a woman to establish a relationship it requires a calculated cost/benefit analysis in order for her to approve it.
Since learning all this thanks to a biology professor at the university I'm majoring currently, I was able to figure out a lot of the stuff that happened in previous relationships and why girls follow certain behavioral patterns. I hope this helps you in some way!