One tenant is moving out

[Mary Mason]

My lease says that the tenants are jointly and severally liable for the rent. One tenant is leaving. I've informed the remaining tenant that he is responsible for the entire rent and he said that he wants to get a roommate. I said the lease does not allow this without written permission from me but I will allow a new person to apply and see if they qualify. I regret saying this because the remaining tenant cannot afford the full rent by himself and it might take more than one month to find a qualified roommate.  I would rather have them both move out and start over. Their lease ends September, 2021.  Any suggestions on how I could remedy this?