Legal Question in Landlord & Tenant Law in Ohio

In Ohio, if there was an oral agreement between you, your roommate, and the landlord that you guys could switch to a new apartment unit, then that will be enforceable. However, proving the term of that new lease agreement may be difficult since it will be you and your roommate's word against the apartment complex. If any discussion of the deal was in writing like an email or letter or any notices from the complex then that would be good evidence for the party trying to enforce the lease for a certain period of time.

However, your making an agreement with your other friend to substitute in for you would have no effect on any contractual relations that you and your roommate have with your landlord. I would note though that if you don't have a written lease then the landlord is going to be hard pressed to prove an anti-assignment or anti-sublet agreement between you (meaning that so long as the new roommate pays all the rent through the end of the term, and returns the apartment undamaged, you are off the hook. If you are going to argue that the new lease is a month to month tenancy, then you might want to read up on how to terminate month to month tenancies. You can find out about that here: http://www.ohiolandlordtenant.com/faq20.html

Lastly, you indicate that the one bedroom you have a signed lease with the landlord for has been leased out to someone else. If that is the case then you will not be under any obligation to pay further on it (though some courts might rule that if that tenant moves out before your lease term would have been up, they may try to come after you. But most courts would hold that once the landlord leased the one bedroom to someone else then that would cancel all of your obligations except to return it in the same condition you received it, normal wear and tear excepted).

When you do leave this place, you might want to take steps to document its condition so you don't get blamed for any damages you did not do. You can read up about your rights with regard to your security deposit at http://www.ohiolandlordtenant.com/faqsecdep.html.