Condition and opportunity, condition and opportunity.
Mate selection is a psycho-biological function that our millenias of evolution has hardwired into both sexes. So internalized and socialized is this process into our collective psyches that we rarely recognize that we're subject to these motivators even when we continually repeat the same behaviors manifested by them. So saying that we're not subject to conditions we're not, or are only vaguely aware of is a bit naive.
It's simple Darwinian logic to follow that for a species to survive it must provide it''s offspring with the best possible conditions to ensure it's survival -either that or to reproduce in such quantity that it ensures survival. The obvious application of this for women is sharing parental investment with the best possible mate her own genetics allow her to attract and who can provide long term security for her and their potential offspring. Thus women are the filters of their own reproduction where as men's reproductive methodology is to scatter as much of his genetic material as humanly possible to the widest possible quantity of fertile females. He of course has his own criteria for mating selection and determining the best genetic hosts for his reproduction (she's gotta be hot), but this criteria is certainly less discriminating than that for women (i.e. no ones ugly after 2am). This is evidenced in our own hormonal biology; men posess 50 times the amount of testosterone women do and women produce substantially more estrogen and oxytocin than men.
That stated, both of these methodologies conflict in practice. For a woman to best ensure the survival of her young a man must necessarily abandon his method of reproduction. This then sets an imperative for him to pair with a woman who will satisfy his methodology. A male must sacrifice his reproduction schedule to satisfy that of the woman he pairs with. With so much genetic potential at stake on his part of the risk, he want's not only to ensure that she is the best possible candidate for breeding with, but also to know that his progeny will benefit form both parents involvement.
One interesting outcome of this psycho-biological dynamic is men's ability to spot their own children in a crowd of other children more quickly and with greater accuity than even their mothers. Studies have shown that men have the ability to more quickly and accurately identify their own children in a room full of kids dressed in the same uniforms than mothers of the child. Again, this stresses the subconscious importance of this genetic trade off.
Social Convention
To counter this subconscious dynamic to their own genetic advantage women initiate social conventions and psychological schemas to better facilitate their own breeding methodologies. This is why women always have the "perogative to change her mind" and the most fickle of behaviors become socially excusable, while men's behavior is constrained to a higher standard to "do the right thing" which is invarably to the advantage of a woman. This is why guys who are 'Players' and fathers who abandon mothers and children to pursue their innate reproduction method are villains, and fathers who selflessly sacrifice themselves financially, emotionally and life decision-wise are considered heroes for complying with women's genetic imperatives.
This is also the root motivation for female-specific social dynamics such as LJBF rejections, women's propensity for victimhood (as they've learned that this engenders martyr psychologies for men's breeding schedules) and even marriage itself.
Good Dads vs Good Genes
The two greatest difficulties for women to overcome in their own methodology is that they are only sexually viable for a short window of time (generally their 20s) and the fact that the qualities that make a good long term partner (the Good Dad) and the qualities that make for good breeding stock (Good Genes) rarely manifest themselves in the same male. Provisioning and security potential are fantastic motivators for pairing with a Good Dad, but the same characteristics that make him such are generally a disadvantage when compared with the man who better exemplifies genetic, physical attraction and the risk taking qualities that would imbue her child with a better capacity to adapt to it's environment (i.e stronger, faster, more attractive than others to ensure the passing of her own genetic material to future generations). This is the Jerk vs. Nice Guy paradox writ large on an evolutionary scale.
Men and women innately (though unconsciously) understand this dynamic, so in order for a woman to have the best that the Good Dad has to offer while taking advantage of the best that the Good Genes man has, she must invent and constantly modify social conventions to keep the advantage in her biological favor.
Reproductive Schedules
This paradox then necessitates that women (and by defalut men) must subscribe to short term and long term schdules of mating. Short term schdules facilitate breeding with the Good Genes male, while long term breeding is reserved the Good Dad male. This is convention and the psycho-social schemas that accompany it is precisely why women will marry the Nice Guy, stable, loyal, (preferably) doctor and still fvck the pool boy or the cute surfer she met on spring break. In our genetic past a male with good genes implied an ability to be a good provider, but modern convention has thwarted this so new social and mental schemas were developed for women.
Cheating
For this dynamic and the practicality of enjoying the best of both genetic worlds, women find it necessary to 'cheat'. This cheating can be done proactively or reactively. In the reactive model, a woman who has already paired with her long term partner choice, engages in an extramarital or pairing, sexual intercourse with a short term partner (i.e. the cheating wife or girlfriend). That's not to say this short term opportunity cannot develop into a 2nd, long term mate, but the action itself is a method for securing better genetic stock than the male provider is capable of supplying.
Proactive cheating is the single Mommy dillema. This form of 'cheating' relies on the woman breeding with a Good Genes male, bearing his children and then abandoning him (again through invented social conventions) in order to find a Good Dad male to provide for her and the children of her Good Genes partner to ensure their security.
I want to stress again that women do not have some consciously recognized, master plan to enact this cycle and deliberately trap men into it, rather the motivations for this behavior and the accompanying rationales invented to justify it are an unconscious process. I fervently believe that for the most part, women are unaware of this dynamic, but are nonetheless subject to it's influence.
For a female of any species to facilitate a methodology for breeding with the best genetic partner she's able to attract AND to ensure her own and her offspring's survival with the best provisioning partner, this is an evolutionary jackpot.
The Cuckold
On some level of consciousness, men innately sense something is wrong with this situation, though they may not be able to place why they feel it or misunderstand it in the confusion of women's justifications for it. Or they become frustrated by the social pressures to 'do the right thing' and are shamed into martyrdom and committed by feigned responsibility to these conventions. Nevertheless, some see it well enough to stear clear of single mothers, etiher by prior experience or observing other male cuckolds saddled with the responsibility of raising and providing for - no matter how involved or uninvolved - another man's successful reproduction efforts with this woman.
The man in this position is (or at the very least interpreted as) a cuckold. He will never enjoy the same benefits as her short term partner in the way of sexual desire or immediacy of it, while at the same time enduring the social pressures of having to provide for this Good Gene father's progeny. It could be argued that he may contibute minimally to their wellfare, but on some level, whether emotional, physical, financial or educational he will contribute some effort for another man's genetic material in exchange for limited form of sexuality from the mother. To some degree, (even if only by his presence) he is sharing the parental investment that should be borne by the short term partner. If nothing else, he contibutes the time and effort to her he could be better invested in finding a sexual partner with which he could pursue his own genetic imperative by his own methodology. It is simply not worth his effort to couple with single mother when compared to a woman without children.
Men understand this instinctively, which is exactly why single mothers need to state things like,
in order to preserve there own gentic viability and the viability of every other woman engaging in the same schema. Anything countering this schema is met with violent opposition as it has the potential to limit what is a very complex, but highly successful social dynamic for women in such a position.