I have a spare moment, so I will do this. I don't expect you will find the argument compelling.
1. The concept that you can "steal a woman's heart from a man" implies a concept of ownership of the woman's heart by the man. Even metaphorically, this is a very toxic sort of thinking.
2. Implying that you should be able to "take possession" of a woman's affection from a man if you find him less worthy only doubles own on the woman's lack of agency in this scenario. That this language is old and from "a different time" is no defense.
3. Implying that this is in fact a good thing because "he abuses her," is a double whammy because it invokes a very negative cognitive resonance with "Why don't those bitches see I am a nice guy" reddit psychology (made famous by the UCSB incident) but also implies that a woman would need rescuing from what the third party man views as abusive because she's not capable of such an escape herself and needs a man to effect said escape.
We can talk about how co-dependency makes 3's secondary point more debatable if you're an expert in that subject matter, because it's morbidly fascinating.
But yes, ultimately "because feminism." Inasmuch as this sort of talk is at least as "offensive" as implying a man "only thinks with his small head." And while equally offensive, it has far more pernicious effects for women in a society that has so much inertia directed towards removing their autonomy (both of body and mind).
Ultimately, I think the author did this by accident. And that accidental misogyny is what I was commenting on. That's what we mean by "internalized". It's so natural that you can use loaded language and actively perpetuate stereotypes without even realizing you're doing it.