I made an oral agreement with a friend to develop software (to be completed in under a year). The contract amount for him was $15K+, of which I paid him 50% upfront (and got nothing for it). I did not pay him the remaining 50% due to failure to perform and started over with someone else. He in turn is threatening to sue me for the remaining 50%. What right does he have to do this in New York considering there is no written agreement and I don't want whatever he claims to have developed?