Eviction questions

You didn't mention how long your lease is supposed to run. If the lease runs through December, then you and the remaining roommates could sue your other for his portion of the rent for December, but it is unlikely that you could force him to continue to pay your share of the rent if you are not married and do not have children together. It sounds like you will definitely have to move at the end of the year. To avoid getting evicted before the end of the year, you should talk to the landlord about some sort of arrangement to pay December's rent. Perhaps he or she will work with you on that since most landlords don't want to have to pursue an eviction at Christmas time.