Lease to Own Question

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I am selling two properties to an investor on a Lease to Own with Option to Purchase contract.  He told me he was going to rent it out, which I agreed to in our contract by deleting the part about him notifying me if he leases the property or assigns the contract. He has turned around, unknown to me until recently, and is selling the property to another person on a Lease to Own contract.  Can he do this?  I still hold the Deed.  Our contract said nothing about him Leasing the Property to Own to another, and he definitely has not assigned the contract, he has written up his own contract with vastly different numbers than he is buying it from me.  Everything I've read online says a buyer in a Lease to Own with Option to Purchase contract cannot sell it to someone else.  It stands to reason because they do not own the property yet.  I need legal advice as he is fighting me on this and I need to know where I stand.  Properties are located in Georgia and Alabama if that makes a difference.

Many thanks in advance!