When you and a roommate both sign a lease, you’re probably expecting to be responsible for half of the rent each month. However, under the terms of your lease, you’re probably responsible for the full amount of the rent in the event that your roommate doesn’t pay her share. Whether your roommate loses her job and falls behind or actually moves out mid-lease and has no intention of making further payments, you may find yourself on the hook for more rent than you bargained for. This is an important consideration when you’re making plans with a roommate: It’s a good idea to make sure you trust the person you’re sharing a lease with, and to put aside a little buffer in case your roommate doesn’t live up to her obligations. If you find yourself in this situation, the first thing you should do is talk with your property manager; the rental office may be able to work with you to find a new roommate or to move into a smaller unit. If you do end up incurring extra expenses because your roommate bailed out, remember that even though you’re responsible to your landlord for that rent, you can still pursue repayment from your non-paying roommate.
Source: http://renters.apartments.com/landlords-leases/can-my-roommate-break-our-lease/