I went through the same ordeal and found a few ways to cope with it.

The very small apartment building I live in is supposed to be smoke free. All the tenants obeyed the rule, until two very inconsiderate guys moved in a few years after I did. They obeyed the rule for the first few months, then they decided to chain smoke in their unit. After they started doing that living here became unpleasant.

I had to prevent the stench from seeping into my apartment, because it was making me ill. Here is what I did:

Sometimes the stench seeps into the hallway. To prevent it from entering my unit, I put a door sealer on the door and weather stripping around the frame.

The three apartments are heated by forced air. A furnace is superb for spreading the stench into all three, because there are some intake vents in the problem unit. I could not stand smoke blowing into my apartment, so I sealed all the vents with foil tape. For heat, I use an oil heater in the colder months.

Now, my place is liveable.

If you cannot do these things, I would move out as soon as possible. Can you sublet?