[Himegoto Jukujo] Shinyuu no Haha wa Hatsujouki

@somnolent1822 It's considered that way when the mother's affection towards her son/daughter and the familial relationship visibly grows cold because of the new sexual partner who is usually a kid their kid's age who will try to monopolize her. Happens a lot in hentai. This series below provides a good example of that (419013, 419017) The mom doesn't need to move out and abandon the kid(s) for that to happen. She could just do shit like forget birthdays, miss graduation day, not cook breakfast for her kid(s), not be around during dinner, and overall stop doing the things/activities/interactions she used to do with her kid(s), etc... because of her new relationship taking up a place in her heart and her time as a mother which inevitably will affect her relationship with her kid(s). Keep in mind I am talking about single and widow mothers here. For married mothers it's 10 times worse as that is cheating on top of NTR and will destroy the family not just make relationships grow colder.

I never got how “stealing” ones mom or sister is considered Ntr , what’s the kid suppose to do sleep with them ? The only time I see it come close is when the mom eventually leaves the household to live with the douche.