Landlords, regardless of the number of units in the building, must treat security deposits as trust funds belonging to their tenants and they may not co-mingle deposits with their own money. If the building has six or more units the landlord must put the money in an interest bearing account.
Even if your landlord has "spent" the deposit, he is still responsible for returning the money to you (less deductions for any damages or unpaid rent) at the end of your tenancy.
If your tenancy is ending, he should repay you. If you are remaining in the apartment, he has violated the law. You may want to consider withholding the last monthâ€™s rent until you get a full accounting for your deposit.
S if the apartment has six units or more he must pay interest.