That may not be the case, if the lease lacks a joint-and-several clause.

This is what our lease says:

MULTIPLE TENANT(S) OR OCCUPANT(S): Each individual that is considered a Tenant(s) is jointly and individually liable for all of this Agreement's obligations, including but not limited to rent monies. If any Tenant(s), guest, or Occupant(s) violates this Agreement, the Tenant(s) is considered to have violated this Agreement. Landlord’s requests and notices to the Tenant(s) or any of the Occupant(s) of legal age constitutes notice to the Tenant(s). Notices and requests from the Tenant(s) or any one of the Occupant(s) (including repair requests and entry permissions) constitutes notice from the Tenant(s).