Women statistically get dumped by husbands at a much higher rate than vice versa with a serious diagnosis. It probably mostly has to do with women being raised as the "caregiver" and when that role is reversed, men don't take it well or as well as women. Probably partly because they already had the role and also because women are raised to give till it hurts to their spouse and kids. When they can't the husband feels neglected or put out by not having his meals cooked or whatever the dynamic change is and it's a recipe for divorce. Leaving an abusive relationship or just having an abuser feel that the victim is getting wise to the tactics, getting "lippy", whatever can make them feel like they are very quickly losing control. I think a lot of people who go through cancer and make it out the other side can also have crisis of faith in their marriage even if they don't get divorced. Maybe they realize that "hey I deserved a bit more empathy here" or "screw that I didn't get better to be a maid and sex doll". I can see that having a turning point in a lopsided power dynamic and people who feel especially entitled to certain things aren't going to take it well. Even without divorce filings abusive people can sense the withdrawal. I suspect and speculate that this is the sort of dynamic that may have been in play here.
Abusive relationships are most dangerous at the very end when the victim is reevaluating and considering those redirects. I don't think it necessarily has to be already filing divorce, but even just questioning status quo can be dangerous.
I think men don’t take good enough care of women who get ill, exactly for the same reason that younger women have a higher risk of being killed by a partner, as it is explained in “Uxoricide” Wiki article.
“The greater age disparity between spouses, the higher risk of spousal homicide. For a male, the damage associated with infidelity is greater when the partner is younger.A woman's fertility decreases as she gets older, therefore, age is key indicator of reproductive success.
As a result, a man will place high levels of importance on a mate with greater reproductive value.”
Because human history is so long, from the evolutionary standpoint, there is not much difference in the thinking of a XXI-century male and, say, Otzi. And a woman who gets seriously ill loses her reproductive potential, or it gets seriously diminished. Hence, she loses her value in the eyes of the partner.
(Ultimately, such behavior of the partners, that today is so self-serving to us, from the evolutionary standpoint, was geared to produce gene diversity. What changed today is the fact that the Earth is overpopulated, so new morality takes over).
A proverb from my mother country, “brother loves sister rich and husband loves wife healthy” illustrates tribal relationships like nothing else.
How does it apply to SM disappearance: BM not looking supportive enough during SM’s cancer treatment, to me, prognostically is not good news.