Are you sure you're not dating my BF? It sounds so like him a few months ago. I met him 5 years ago and we both had our own places. Mine was tidy like a Japanese garden, his was a stinky brothel. We moved in together 4 years ago and things declined in the cleaning dept. I tried not cleaning and did not work; I tried yelling and (duh!!!) did not work, I tried asking nicely and did not work. This year I took off to prepare for GRE, Gradchool aps, etc... So he's out working and I'm in the house and take care of much of the cleaning...All I demand from him is 1) keep things clean; it shows respect for my house work; 2) when I ask you for a chore, do not do it at your leisure (i.e., a month later), do it NOW. I tried in the past discussing my worries with him. I told him (and I firmly believe this) that doing 1) and 2) is a way of showing love and respect in our everyday dealings. He told me that being "messy" was his nature, which is a bunch of bull. Eventually sh$t his the fan for a different reason and the issue was brought up again and this time it clicked. We had a serious discussion about how what he call "little things" matter and are the meat and bones of a relationship. I made him understand that his disregard for 1) and 2) was equivalent to me blowing his salary on heels. So, my advice is to have a serious conversation that would make him understand the magnitude of the issue.
Good luck!