I have exactly the same problem Shables and it really gets me down.
I've always been a bit untidy myself, in regard to filing letters away, putting washed clothing away, but since moving in with my partner, it's become a joke.
He's obviously never had to do anything for himself, so clothing he takes off ends up on chairs or the floor, all his letters and documents are thrown wherever, the hob is always covered in his paperwork, every part of the house is used as his own personal dumping ground.
At the moment, there are 26 empty coke cans in his office and several more deposited around the house. He could be standing next to the bin, yet any rubbish will be thrown down where he fancies.
I really cannot cope and hate living in a pig sty.