Now, now, Amos! The reasons of the heart won't change much in a dozen generations or so! Are "ancient" people so different that humans reproduce differently this century?

Cultural differences between us and our ancestors are real, but no wider than those between many people living today. Cultures constrain our emotions and reactions into diverse patterns, and we describe our values and options with slightly different language, but whether you call a situation True Love or Stockholm Syndrome, the behaviour and many of the emotional reactions may be the same.

In this case, the cad appears more precious in retrospect, and her dream of him has outlasted her anger at him. Evidently she never stopped thinking of him as a romantic figure, maybe because he never stayed around long enough for glamour to be replaced by mundane experience.

Also, by this point in the story she has experienced the shame and poverty of being an unmarried mother, and she has not yet experienced the misery of a bad marriage. Right now, to her the grass looks greener on the other side of the fence.

I agree with Dave Hunt that the "six months" was supposed to be an impossibly short pregnancy. Some people just don't know the score, even today after many taboos have broken. The "Young Billy Brown" version's biology is better.