I get that marriage implies caring for a sick partner and so, but in today's world, that promise don't really have any legal weight... it can be abolished for any reason, and many more people don't marry anyway, so such promise to care for a partner is only a vague expectancy.

Now, I agree that men leaving their sick women is evil, but it makes perfect sense in a non-moral context.

Women here often are proud to admit they choose men that are only the best of the best (such as top 20% of men), dehumanizing other men, and they sincerely believe they deserve top men and are at their level (they aren't). However, those top men have options and they are freer to leave and find another healthier and younger woman. Those men also have a wider age range they can date and be fertile.

So yes, women are free to choose to fuck the same 15% of men, but they are not entitled to those men's care or commitment or loyalty, and there is no incentive to those men to stick to those values as long as they have options. In utilitarian terms, Why stick with a sick dying woman, if you have 2 other options waiting for you?

This just shows that in this dating environment, men pre-suffer, while women post-suffer.

It makes sense the universe is not only unfair to men on dating, it would be unsustainable long term. I would say most men suffer more in lack of options, while women suffer more in consequences of their choices.