looking for mangas with highly unhealthy relationships. it can be where the female lead is kidnapped and mentally/physically tortured by the male, or where the male threatens to murder her whole family if she doesn't cooperate with him for example. I don't mind it if there's love involved between the two, but there has to be sum sick and twisted in their relationship.

it'd also be better if they stay together till the end, not that one of them dies.

Someone recently made a similar thread you may want to check out: https://www.mangaupdates.com/topic/vhyxiye/looking-for-toxic-relationship-manhwa

These are the only things that come out and I am not really sure if these fit your desc.

School Days
Die
Fetish
Hitsuji no Uta
Sekai no Hate
Lady Devil. This one is manhwa but pretty good.

Flowers of Evil
Aku no Hana

These possibly aren't twisted on the level that you're looking for though, based on your examples.

Also re Flowers of Evil:

One of the characters dies in the last chapter.