Just something I've noticed over the years.

In relationships where the man loves the woman more, he puts more effort into the relationship. When the man knows that the woman has other options, he is more likely to invest his time, money, and emotional effort, because he wants to impress her. He is more likely to propose marriage and he is more likely to be faithful to her, because he knows that if he fucks up, she's out the door. Such couples tend to be happier, generally speaking.

In contrast, when the woman loves the man more, or is more invested in the relationship than him, these couples are often miserable. When the man believes he has other options, he is more likely to cheat and less likely to propose marriage. He usually sees his current partner as a placeholder from which he can get regular sex and emotional/domestic labor, until his dreamgirl comes along, at which point he will not hesitate to "trade up" and discard his forever girlfriend. In the meantime, he will only invest the bare minimum effort necessary to hold on to his sex/cooking/cleaning appliance. He doesn't think it's important to put much effort into such a woman because he doesn't see a future with her, he is only with her for convenience's sake.

This is why FDS tells women to dump any man if you aren't his dream girl. If you love him more than he loves you, your relationship is doomed. Nothing you can do or say will change his mind, and in the meantime he will be happy to use you for the services you can provide for him, until a better woman comes along. If you can't find a man who loves you more than you love him, it is better to remain single.

"Nothing but the deepest love will induce me into matrimony"

-Elizabeth Bennet, Pride and Prejudice.