The landlord declares the forfeiture of my lease and evicted me because I didn't pay the rent for next month. I paid the rent for this month. I vacated the apartment and returned the keys to him as he required. But the landlord said that I was still bound to the lease. So I have to pay the rent when the apartment is not occupied. Do I have to pay the rent?
You will likely be legally bound to pay the rent for the term of the lease, or until the landlord releases the apartment. The landlord must make his best efforts to market and release the unit, called mitigating his damages. But if he is not able to rent it out again, you will likely be liable for the whole term. In order to enforce this, however, the landlord needs to file a civil suit. Often times you can negotiate it or the landlord may not even try to enforce it if you don't have the money to collect. Consult with a debt or landlord/tenant attorney for more information.