http://therationalmale.com/2015/08/11/post-selection/

Dumping a woman is the highest form of social proof for a man.

In no uncertain terms he demonstrates to her that he has the supreme confidence he can find another woman with better prospect than her. Even if this isn’t the pretext of the breakup, this is the message in the medium that she understands; she doesn’t measure up to his expectations.

This then is further compounded by the unconscious knowledge that it should be women who are socially in charge of the sexual selection and approval process. When a man dumps a woman he demonstrably takes that agency away from her.

However, the effectiveness of that social proof for the dumped woman is only proportional to the doubt that he may have been a better, more optimal Hypergamic choice for her. We understand the effectiveness even a fabricated perception of preselection has on women, but depending on the psychological impact a man has, post-selection and the uncertainty of his long term fitness can be so powerful it can create an Alpha Widow of her.

Hypergamous doubt makes women creatures of constant comparison. Thus, when (if) she makes another intimate connection after that breakup, the new guy is held next to the comparison of the previous one. Once that comparison is made, that post-selection value of the previous guy (or lack thereof) becomes reinforced for her.