No, you cannot terminate the lease without penalty: you and your grandmother are liable for all rent due under the lease for its full remaining term or duration, even if you are suffering abuse. The lease is a contract between you and your grandmother on the one hand and the landlord on the other; that contract is not affected by what another person who is not a party to the lease does, and the fact that your boyfriend may be abusing you is not, to be blunt, the landlord's fault, issue, or concern. The landlord's right to the rent is not affected by what is happening bewteen your boyfriend and you.