You and your new roommate must also sign a new roommate agreement (with all other roommates on the premises). The co-tenant agreement should be kept up to date so that it matches the details of the lease. The agreement describes the terms, conditions and responsibilities agreed upon by each of the residents. Colocation contracts are sometimes referred to as colocation contracts. LawDepot provides a written colocation agreement. As a last resort, you and your roommates may have the right to sue your outgoing roommate over the money you pay to cover the rent he/she would have paid. If you have entered into a written or oral agreement that you will all remain in the apartment for the duration of the lease, you can sue this roommate for breach of contract or contract. If you clearly mention this issue in your colocation contract, it is all the better for your legal protection. 4. Surety.