You may not need a license in NJ to rent out a room. You were not actually renting out an apartment, but had a room-mate. It would be worth looking into what the law requires in more detail. It could be you are perfectly legal and can go after the roommate for the last months rent.
I found information on rooming & boarding homes here
http://www.lsnjlaw.org/english/place...teen/index.cfm
A license is still required along with annual inspections and giving the tenant a copy of their rights and a few other things. It looks like New Jersey's landlord tenant laws are extremely in favor of the tenant, just as they are in California. I expect this will have a negative effect on the availability of housing. I can't imagine why someone would want to be a landlord with such onerous legal requirements imposed on them.
You would be better of writing off this loss and moving on. If you take on a new tenant, make sure you understand the laws next time.