In a March 19, 1980, letter to an SP fan, Mary Ann Montgomery, who became Aurelia Plath's penpal, Aurelia has just described her California honeymoon in 1932 and her and Otto's decision to live back East. It continues with what she imagined family life would be like:
"I loved [my parents] and took them for granted--after all, I knew nothing else but that we were close, enjoyed each other, which I thought was the essence of most family life. Oh, what hard lessons lay ahead--what shocking, terrifying revelations. My husband never knew love in his family; I was ready to share all of mine with him. I never witnessed jealousy before, distrust, possessiveness--all augmented through untreated diabetes that I did not know existed within him. On the outer personality, high idealism, honesty--oh, well, why dig into the past? It would take forever to give a complete picture and then who ever knows another completely or is competent to judge. The thing to do is remember what was good and go on with that."
Sylvia Plath must have witnessed a jealous, distrustful, possessive marital dynamic in her family home -- born as she was 10 months after her parents' wedding. That could explain a lot.