What can happen to me if I have been bumming on a buddy's couch and the landlord is ticked off?

I stayed with my friend in upstate NY for about 3 months while searching for my own place. His landlord caught wind (probably from complaining neighbors, we were a little rowdy throwing parties and what-not) and is now causing a lot problems for him as he moves out. What, if anything, can the landlord legally do? Can they take him/us to court or sue? They say they have proof but then they say it went on for a full year, which is completely false.