Two tenants - can one terminate the lease for both?

[Paul Hormann]

I have a rental with a couple on a month-to-month lease.  The couple broke up and the woman moved out and now she wants to terminate the lease, but the guy wants to stay. Can one tenant terminate the lease for both tenants?  And would I have to return the security deposit and get a new one from the remaining tenant?  The tenant who wants to remain may not qualify on his own...