My friend lends money from me for his business and is not paying bacK

My friend owns a Resturant and I joined him to increase his orders. After 2 months he left and told me that some personal family matters are going on . he asked me to take care of the restaurants and come every month , hold the salaries of the labour and then returns back. I pay his debts after he promise to return them back now the Resturant is closed and I never asked him to buy the Resturant . now all his dues are paid and he is not accepting to pay me back my mind and is saying that when he is not present he has no reason to pay back the money . the amount is quite high for me. What should I do . neither we signed an agreement in written but I have witnesses to support my statement.