No, this is not a reason to forgive the rest of the lease. The lease is a contract between you and the landlord: as long as the landlord honor's the landlord's obligations (providing you a habitable place to live), you are held to your obligations (rent for the entire term of the lease). Events over which the landlord has no control or responsibility, like your admittence to residential drug treatment, do not affect your contractual obligations to the landlord.