My XABF smoked meth. It is a nasty drug with really bad side effects. I'm not sure how long he's been doing it but my ex started off snorting it then eventually moved to smoking it. It took me a long time to see the side effects of paranoia, irrational behavior, staying out all night, even for him to lose his job. He used it for years before that stuff ever happened. BUT once it did there was no going back! I wish I had known early on. My XABF used to give me money as well and made it seem like he couldn't be doing anything wrong because he didn't have any money. What I have since learned is that meth is "a poor man's drug" and his friend told me once that $20 is enough to last a while. Not a long while especially as his tolerance grew but scraping up $20 isn't that hard usually. I also found out (the hard way) that you can trade almost anything for drugs. He had clothes coming up missing that his best friend said he probably traded for drugs. Not even good clothes.
As far as living together I would not recommend it long term. Do whatever you have to to get out on your own. While you say now that it would be living separately think about the effects on you. Would you knowingly have a roommate with those behaviors? If it were me I could see myself getting sucked back into the drama of it all. I had to go no contact completely. Pack his things, make him leave and go no contact.