In theory you cannot use your security for rent during the tenancy. That having been said, if you owe rent at the time you leave, the security can be applied to it. Given the notice provision, you may be on the hook, but I can not say if you LL will chase after you
It would be hard to answer your question without reading the lease. Each lease is very different and there really is no such thing as a "standard lease."
Also, a lease is a written contract. There are many ramifications because of that. (such as a subsequent oral agreement may not be enforceable).
You may want to immediately contact an attorney before there is a problem rather than later.
Some offer free 30 minute consultations.
no attorney client relationship has been formed.
Unfortunately it is not uncommon for tenants to use their security deposit for the last month or two of rent, but legally, the security deposit is security to make repairs if you cause damage to the premises. If a landlord takes the security deposit, you have a claim against the landlord, plus treble damages if not returned to within the statutory period less any costs of repairs.
To protect itself, the landlord would need your consent to not return the security deposit and/or a court order stating that the landlord is entitled to a judgment against you, which may be satisfied by keeping, rather than returning, your security deposit.
The forfeiture language is probably not enforceable unless the landlord can demonstrate the landlord made every effort to mitigate its damages and was unable to lease the apartment.
The foregoing is not intended to be legal advice upon which you may rely as I have not been retained for this purpose.