You sue him--that's the only way to get back your money if he won't return it. You would sue him on several different grounds, such as--* breach of contract--violating the oral agreement;* conversion, which is basically theft--keeping your money which was entrusted to him* unjust enrichment--it is wrong to let him keep your money without you getting anythingAct quickly, before the money disappears (if it hasn't already)--you can only get the money back if it's there or the erstwhile partner otherwise has the money to repay you. For this amount of money at stake, you are strongly encouraged to retain an attorney to help you.