Could be worse. You could be this gal. https://able2know.org/topic/529484-1#post-6891148
So here's the deal.
You will clean up after him forever. He's not about to change.
Or, you could stop cleaning up and wallow in the same filth with him. If you haven't already seen rats, mice, and/or roaches, then you will then.
Plus there's the fun of breathing mold-infested air, which a lot of people are sensitive to.
So them's your choices. You either resign yourself to being his maid, or you embrace the filth and the rat bites (oh yeah, rats bite. Ever heard of Hanta virus?).
I suppose a third option would be to hire a cleaning service. If you go that route, then be prepared to pay whatever the hell it costs, on a regular basis. And since your BF doesn't see anything wrong with how he's living, don't expect him to defray any of this non-tax-deductible cost.
If you go Option #3, then you're automatically setting fire to a few thousand dollars, every single year, in perpetuity. Consider that a part of your rent, so if you're moving in with him to save $$, think again.
Personally, I am not exactly a neat person, but I am also absolutely not on the filth side of the equation, either. This setup would drive me nuts and, like I said, it's not like I feel the need to do a white glove inspection or anything. But I'm kinda funny about not giving aid and comfort to pests.
So decide which of these options appeals the most to you (or you hate the least). Or do the easier, helluva lot more sensible thing, and tell him you're not moving in with him, period, end of story. Be mentally and emotionally prepared for that ending it, for it might.
And another thing.
Issues with hygiene are often a sign of mental illness. See (among many other sources; this one's a quick read): https://en.wikipedia.org/wiki/Self-neglect
Hoarding is also a sign of mental illness. See: https://en.wikipedia.org/wiki/Hoarding#Human_hoarding
If I were you, I would run, not walk, away from this trainwreck.