Landlord suing after asking me to move out?

[Ashley C]

Long story short, my apartment became unlivable a year after signing a two-year lease. Since the landlord wanted to demolish the place soon anyway, he asked us to switch to a month-to-month verbal and move to a new building, and we did. The living there was terrible, so I gave a month's notice in writing that I was moving out as state law prescribes.

Now he's threatening to sue me for the unexpired rent on the two-year lease for the place he moved us out of!

Now, I've gotten basically two answers from people on this:

1 - He can't do that, because we both agreed to break the lease, and there's tons of proof.

2 - He CAN do that, because the new building can be considered "substitute housing" under the two-year lease.

I have read and re-read Wisconsin state laws and have yet to see anything about "substitute housing" in them. Does anyone know about this in Wisconsin? I don't want to believe it, but I don't want to discredit it either just because I WANT to believe I'm safe. :P

The 2-year lease specifically had the address of the first apartment, and didn't say anything about moving us somewhere else if necessary. I see no provision in here that could back up a claim that the second place was "substitute housing."