I just typed out a whole response to this but it's gone now so I'll refer you to pgs 63-64 of Parallel Lives
- Abby was 37 at the time of her marriage to Andrew, decidedly a spinster by 1860s standards
- Andrew had no sexual contact for at least four years prior to marrying Abby
- Andrew & Abby shared a bed despite it being much more common for married couples to have separate beds. This could be either out of necessity or it could point to their marriage indeed having been affectionate in nature.
- Despite it being very common for widowers to remarry and have a child within a year of remarrying, Andrew & Abby never had children. We have no evidence either way as to the couples' fertility at the time of their marriage but Andrew did father three children with his previous wife and Abby's autopsy says her fallopian tubes and ovaries were fully intact. So either they were infertile or they did not consummate their marriage (which would be exceptionally odd). To boot, having a child of her own with Andrew would've cemented her place as the new Mrs. Borden as the mother of his child rather than the much more tenuous position of step-mother.
- Emma did not like Abby from day 1, she viewed her as trying to usurp both her mother's place and her place as Lizzie's mother-figure
- Emma is shipped off to boarding school for a year at the age of 16. She only stayed a year despite making friends and by all accounts having a good time (was she worried about her sister?). We don't know if this was Emma's decision, a mutual decision, or a decision imposed on Emma by Andrew.
- Also the relationship between Lizzie and Andrew is repeatedly marked in PL and elsewhere as having been a "special love" - I don't know if this is a common description of close parent-child bonds from the time but that is certainly worth further examination.