Roommates: I Co-Leased a House with a Friend, and He Wants to Add a Third Roommate

My question involves landlord-tenant law in the State of: Georgia

I co-leased a house with a friend, and he wants to add a third roommate. I decided against it, but he went ahead and talked to the landlord. Can the landlord and my co-tenant bring in this new roommate without my consent, even though we both signed the lease? What are my next steps?

Roommates: I Co-Leased a House with a Friend, and He Wants to Add a Third Roommate