I still don't get the idea why yanderes want to just kill their partner. I mean it is understandable(?) if the partner cheats, but it is not like the partner is cheating anyway.
@nawoon
There's also the notion that if you destroy something it will be forever tied to you.
See Hoshi no Samidare (Lucifer and the Biscuit Hammer) for a lucid example of this. (And just in general, as it is one of my few 10/10 mangas.)