Thanks for your question.
The position is that you are bound to pay the rent until you terminate the lease in accordance with a break clause in your lease (if there is one) OR until you arrange a surrender of Lease with the landlord OR when you are entitled to terminate the lease because of a breach of contract by the landlord which is so serious that it goes to the heart of the lease so as to substantially deny you the benefit of the contract (this is called a repudiatory breach.
Unless you terminate in one of the above ways they will be able to sue you for the rent up to the end of the term.
Check your lease for a break clause.
It does not sound as if their lack of maintenance is denying you the whole of the benefit of the lease but you may consider speaking to other owners of units and seeing if they want to write a collective letter to the landlord stating that they are in breach and asking that it is remedied otherwise you shall pay for contractors to remedy the lack of repair and then sue them for the money.
A formal surrender of tenancy with the landlord whereby you both agree and accept that the tenancy shall cease earlier than the fixed term and you shall leave the property. This would be a formal agreement in writing and the landlord will ask you to pay a fee for this. The amount of the fee would be for you both to negotiate, but obviously you should negotiate for considerably less then the rent that you would pay up to December.
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