I remember there was this married couple and the husband gets mad and kills the wife then dumps the body somewhere in a landfill.The next day he finds his wife back home like nothing happened. He kills her again and this goes on for a while. He thinks he's going mad and I'm not sure but the wife experiences the same thing? And at the end there are many bodies of eachother. Now thispart I dunno if it's from another manga or the same one but I remember 2 siblings,a boy and a girl no older than 9 playing there in the landfill . I think they take home a body part or something like that? I also remember there was another murder and i'm pretty sure this detective came to the childrens' house and asked them some questions.

That second part sounds weirdly like a scene from Higurashi no Naku Koro ni - Onikakushi Hen and its associated series, though I've only watched the anime. Unfortunately, there's nothing like the first half of your scenario in it.

Land of the Sacred Spirits in Keep on Vibrating. (I am hardly a fan.)
I couldn´t remember on my own and typed in "manga killing his wife in a landfill" into google. It got the result as the 2nd hit and your (?) yahoo question as the first.
Yes, research with descriptive attributes is really that easy.

I also read EU/US comics and am a librarian.
Manga-Masters, My ANN-Lists + Imdb