Go ahead and get this guy to give you a full copy of your source code as it now stands. Since he did not finish the project in two months as specified in the contract - you have a written contract, right? - you can terminate the business relationship on the grounds of breach of contract. There should be no need to reverse engineer software that you paid for. The nature of the business relationship here is that you own full rights to the software. Best of luck to you as this sounds like it will be a real pain to resolve.